Maṇḍala or Sign? Re-Examining the Significance of the “Viśvavajra” in the Caisson Ceilings of Dunhuang Mogao Caves ^†

Abstract

This article delves into the exploration of a significant sign, the “viśvavajra”, found in the caisson ceilings of Buddhist esoteric art in Dunhuang’s Mogao Caves. These caissons, featuring the viśvavajra sign in the center, were prevalent from the mid-Tang period to the Western Xia dynasty (ninth to thirteenth centuries) and are recorded by The Overall Record of Dunhuang Mogao Grottoes under description as “Jiaochu Jingxin”. Similar caissons are also found in Western Buddhist Caves near Dunhuang, and Yulin Caves in Guazhou County, indicating a distinct regional character. Focusing on a well-preserved and intricately detailed example from Cave 361, this article aims to elucidate the specific tantric significance of the viśvavajra at the center of the caissons within the broader context of Buddhist art. Drawing from related tantras, the discussion explores how the sign and its surrounding compositions align with a particular homa (fire offering) maṇḍala, specifically the śāntika maṇḍala crucial to numerous Tantric Buddhist rituals. Furthermore, the article examines the evolution of caisson of this type of maṇḍala over time. By comparing the mid-Tang example from Cave 361 with the late Tang period’s Cave 14, a noticeable shift in format becomes apparent. The viśvavajra sign takes on new significance, embodying “the samaya of all Tathāgatas”. Ultimately, the article explores how the significance of the viśvavajra sign transforms into an allusion to Vairocana or Rocana under the Sino-Tibetan Esoteric Buddhist context in the Hexi Corridor during the early Northern Song and Western Xia dynasty.

1. Introduction

The viśvavajra, also known as karmavajra, consists of vajras arranged in a cross formation, typically featuring three, five, or nine prongs in its depiction. It typically functions as a ritual object or a philosophic sign in Tantric Buddhism. This article will delve into the significance of the viśvavajra as a recurring Buddhist sign, particularly its frequent appears in the caisson ceilings of Dunhuang Mogao Caves, Yulin Caves, and Western Thousand Buddha Caves, for instance, Mogao Cave 361, Yunlin Cave 21, Western Thousand Buddha Cave 18 (Figure 1a, Figure 2 and Figure 3) along the Hexi Corridor in China. These caves date from the mid-ninth to thirteenth centuries, corresponding to the mid-Tang period (766–836 CE) and Tibetan rule over Dunhuang (786–848 CE), to the Western Xia dynasty (1038–1127 CE). The caisson, conventionally described as a square box-like structure used in traditional Chinese ceiling construction, takes on a specific role in the structure. It constitutes the top part of the ceiling, often referred to as the “ceiling well” (zao-jing 藻井). The well in the ceiling serves not only as a decorative or structural element for the entire cave, showcasing religious prestige, but also as a notion for “containing water plants to prevent fire”, a crucial aspect for the cave’s safety (Y. Shen 2011, p. 519).1 While the caisson ceiling finds extensive use in palaces and temples throughout China, the specific type of caisson featuring a viśvavajra at the center is documented in The Overall Record of Dunhuang Mogao Grottoes (Dunhuang Mogaoku neirong zonglu 敦煌莫高窟內容總錄) under the description “jiaochu-jingxin” 交杵井心 (Dunhuang Academy 1982, p. 5). Here, the term “jiaochu” refers to viśvavajra, and “jingxin” denotes the center of the well-like caisson. This particular caisson ceiling exhibits a distinct regional character, with very few examples found outside the Hexi Corridor, for instance, at Alchi Monastery in Ladakh.

While some caissons found at Yulin and the Western Thousand Buddha Caves exhibit similarities, the majority are concentrated in the Mogao Caves. Specifically, Caves 7, 361 (Figure 1), and 370 from the mid-Tang period, Caves 14 (Figure 4), 30, 140, and 177 from the late Tang period, Caves 243, 289, and 364 from the Northern Song dynasty (960–1127 CE), and Caves 87 (Figure 5), 291, 326, 328, and 382 from the Western Xia dynasty all exhibit the same sign in their caisson centers (Dunhuang Academy 1982, pp. 1–176). Most of these caves are situated in the northern end of the southern area of the Mogao Caves, with the exceptions of Cave 140 and 177. According to the research by Zhao Xiaoxing from Dunhuang Academy, she asserts that the caves in the northern end were intentionally designed as Tantric Bodhimaṇḍas (Zhao 2017, pp. 534–35). The author supported her statement through investigation.2

This article will primarily focus on the caissons of Mogao Cave 361 and Cave 14, as they represent early types among all the caissons, featuring well-preserved states and the richness of their iconographic details, potentially linked to maṇḍalas, which distinguish them from other homogeneous caissons. The caisson of Cave 14 exhibits a clear evolution from that of Cave 361, with the unique feature of a five-pronged viśvavajra positioned at the center, suggesting a connection to the concept of the “five wisdoms.” Other caissons may resemble Cave 361, though many are obscure and lack sufficiently comprehensive information, as exemplified in Cave 87 (Figure 5).

2. The Rising Attention

The viśvavajra, an ancient sign, first appeared as a relief on one of the pillars in the caitya cave of the Bhaja Caves in Maharashtra, India. This relief is believed to date back to the second to first century BCE. J. Fergusson and J. Burgess, notable scholars in the field, made this assertion (Figure 6). Fergusson’s description depicts the image as comprising four triśūlas (Fergusson and Burgess 1880, p. 225), yet it is named viśvavajra when recorded by The Huntington Archive of Ohio State University. In the first century BCE, Buddha images had not yet appeared. In the caitya halls, the stūpa was typically used to symbolize the Buddhist dharma. Alongside the four-triśūla relief on the columns were other reliefs, such as the lotus flower and the dharma wheel, all related to Buddhist iconography (Fergusson and Burgess 1880, pp. 223–28). This seems to be the only surviving instance in early Indian Buddhist art. The four-triśūla motif is relatively rare and was not extensively employed in early Buddhism. In this case, it either emerged as a distinct Buddhist symbol or appeared alongside other Buddhist signs.

The Interpretation of this Image, whether It symbolizes a maṇḍala metaphor or simply serves as a sign, remains contentious among scholars. Several scholars have posited the notion that the viśvavajra sign may constitute a central component of a maṇḍala, a theory fraught with historical ambiguity and scholarly debate.3

Figure 6. Four-triśūla figure on the pillar of the caitya cave, second to first century BCE, Bhaja Caves, Maharashtra, India. Collected by The Huntington Archive.4

Figure 6. Four-triśūla figure on the pillar of the caitya cave, second to first century BCE, Bhaja Caves, Maharashtra, India. Collected by The Huntington Archive.4

Among the earliest and most contentious examples of such caissons featuring the viśvavajra sign is Cave 361 (Figure 1a), a diminutive chamber spanning less than 10 square meters. Originally constructed during the mid-ninth century, toward the end of Tibetan rule over Dunhuang, Cave 361 underwent subsequent renovations during the Five Dynasties period (907–960 CE). Despite its construction under Tibetan rule, the artistic motifs adorning the cave, including murals and painted figures, predominantly exhibit characteristics associated with Sino-Buddhist artistry.5

Of notable interest are the mural compositions on the southern and northern walls, which predominantly feature sūtra-based imagery (jing-bian-hua 經變畫), while the eastern wall is adorned with tantric iconography.6 This juxtaposition of exoteric and esoteric Buddhist imagery imbues the cave with a profound synthesis, conceptualized as a “harmony of exoteric and esoteric Buddhist cave” (xian-mi-yuan-rong 顯密圓融), further emphasizing its cultural and religious significance within the broader context of Buddhist cave art.

Several scholars have presented diverse interpretations, with Guo Youmeng 郭祐孟 and Zhao Xiaoxing 趙曉星’s being the two most frequently cited. Guo Youmeng posited that the viśvavajra sign primarily symbolized one of the unique manifestations of the Vairocana maṇḍalas (da-ri-bie-tan 大日別壇) in Shingon Buddhism真言宗, specifically representing Vairocana (Guo 2009, pp. 143–74). Yin Guangming 殷光明 (1957–2013 CE), a researcher at the Dunhuang Academy, echoed this conclusion in his work (G. Yin 2014, pp. 7–20). Conversely, Zhao, also affiliated with the Dunhuang Academy, criticized Guo’s assumption that the viśvavajra sign suggests Vairocana. Zhao argues that the viśvavajra, denoting the four directions as the “cross-vajra throne” within the Vairocana maṇḍalas, represents the fundamental foundation of the Buddhist cosmos rather than Vairocana himself (Zhao 2017, p. 297). She identified the twelve heavens surrounding the central viśvavajra within the four grooves as comprising a typical Buddhist “twelve-heaven maṇḍala” (Zhao 2017, pp. 289–95). According to her succinct analysis and quotations from Robert Beer (2003, p. 95), the central three-pronged viśvavajra sign holds the significance of “the twelve nidānas” 十二因緣 (twelve links of dependent origination) and could also be regarded as the cross-vajra throne protecting the entire cave (Zhao 2017, p. 297).

The author agrees with the identities of the twelve-heaven figures she identified, but the possibility of them forming a maṇḍala, as well as the role and significance of the central viśvavajra, warrant further discussion. Since the caissons are formed and depicted very similarly with only minor distinctions, they should have closely related religious explanations. Additionally, at least four caissons with a viśvavajra sign in the Mogao Caves (Caves 14, 140, 326, and 382) are inclined at a 45-degree angle. The caisson in Cave 14 features a five-pronged viśvavajra, not a three-pronged one. These differences make it difficult to link them to a cross-vajra throne or symbolization of the twelve nidānas.

3. Why Maṇḍala?

According to Zhao Xiaoxing, the entirety of the caisson in Cave 361 represents one of two deliberately constructed as a maṇḍala, the other being found in Cave 7. However, the remaining caissons, numbering more than ten, featuring the viśvavajra sign within the Mogao Caves, cannot conclusively be deemed as explicit maṇḍalas (Zhao 2017, pp. 309–11). This uncertainty arises primarily due to the limited iconographic details preserved within these caissons, particularly the absence of the “twelve-heaven” motif, which is traditionally considered the central theme of caisson maṇḍalas.

The number of maṇḍala sketches dating back to the Tang dynasty (618–907 CE) and unearthed from the Dunhuang region is considerable. Among these, an exemplar preserved by the British Museum (Figure 7a) serves as a notable illustration. This particular maṇḍala, excavated from Dunhuang and dating from the latter half of the ninth century, is structured into three distinct layers, adhering to the conventions of Chinese Buddhist artistic style. The central portion of the maṇḍala features a lotus umbrella, signifying its symbolic significance within Buddhist cosmology. The middle layer is delineated in a square shape, with four heavens and deities including Brahmā and Indra positioned at the corners, each side marked by a corresponding Chinese character denoting the four cardinal directions. The outer layer of the maṇḍala is meticulously adorned with detailed depictions of the four heavens and their respective directional counterparts, meticulously rendered on the four doors and corners. This maṇḍala is revered by the twelve heavenly attendants, further emphasizing its religious and ritual significance. The southwestern boundary corner of the entire maṇḍala (Figure 7b) is specifically designated as the entry point for the dhāraṇī preacher (zhou shi 咒師), namely the guru, demarcated by the inscription of Chinese characters “zhoushi churu” 咒師出入. Noteworthy is the intricate detailing between the outer square layer and the middle square layer, where meticulously painted ruled ink lines converge, creating a sense of depth and perspective. Given its meticulous design and elaborate symbolism, it is plausible that this maṇḍala sketch may have served as a blueprint for the creation of a caisson, a common architectural feature in Buddhist cave art.

For example, Cave 361 (Figure 1a) exhibits a configuration reminiscent of the aforementioned maṇḍala sketch (Figure 7a). The central portion features the viśvavajra on a lotus-enclosed circle, followed by lotus petals at the four corners, while the outer layer showcases the twelve-heaven motif.

The caissons in the Mogao Caves featuring a viśvavajra sign in the center can be classified into three types. The first type comprises a three-pronged viśvavajra at the center, surrounded by twelve heavens, constituting the entirety of the caisson. An exemplar of this type is found in Caves 7 and 361 (Figure 1a). The second type showcases a five-pronged viśvavajra combined with four directional Tathāgatas at the caisson, accompanied by three buddhas with thousand Buddhas painted on the four slopes. Among all the Mogao Caves, only Cave 14 (Figure 4) conforms to this category. The final type features solely a three-pronged viśvavajra at the caisson, accompanied by depictions of four or ten directional Tathāgatas, a thousand-Buddha motif on the four slopes, or a “circular floral pattern” painted on the four slopes, as exemplified by Cave 87 (Figure 5). Most of the caissons fall into this category, although this last type lacks explicit indications for scholars to identify a specific maṇḍala. However, apart from Cave 364 from the early Northern Song period (tenth to eleventh centuries), which features a plain square ceiling, other caissons with a viśvavajra exhibit a striking resemblance to Cave 361. The subsequent discussion will delve into whether they portray a particular maṇḍala.

4. Which Maṇḍala?

4.1. The Directions

To summarize (refer to Figure 8a,b) Zhao Xiaoxing’s conclusion, the depiction of twelve heavens at the four grooves of Cave 361’s caisson suggest the presence of a “twelve-heaven maṇḍala”: the eastern groove features the sun Sūrya seated on a five-horse chariot (E1), Dhṛtarāṣṭra playing the pi-pa lute (E), and the moon Candra seated on a five-goose chariot (E2); in the southern groove, the fire deity Agni (S1), Yama, the lord of death (S), and Brahmā (S2) are depicted; the western groove portrays Nairrtī wielding a knife (W1), Varuṇa holding a snake (or dragon, W), and the wind deity Vāyu (W2); the northern groove features Īśāna holding a single trident (N1), Vaiśravaṇa, the guardian of the north (N), and Vasundhara, the god of the earth, holding flowers (N2) (Zhao 2017, pp. 289–95). However, she points out that, besides the four cardinal Heavenly Kings, it is observed that only the northeastern guardian-heaven, Īśāna (N1), is depicted at his proper direction, whereas the others do not consistently align with their respective orientations (Zhao 2017, p. 302).

Questions arise. Upon examining maṇḍala sketches from the Tang dynasty in The Images of SAT Daizōkyō (Taishō shinshū daizōkyō zuzōbu 大正新脩大蔵経圖像部) (Figure 9) edited by Junjirō Takakusu 高楠順次郎 (1866–1945 CE), the central yidam of a so-called twelve-heaven maṇḍala is typically depicted as either a two-armed or four-armed Acara (si bi bu dong 四臂不動), rather than a viśvavajra. Furthermore, it has been observed that at least four caissons with viśvavajra inclined at a 45-degree angle are found at the Mogao Caves, as evidenced by Cave 14. These inclined formations cannot be readily construed as cross-vajra thrones. As master Yi Xing 一行 (683–727 CE) said in his Commentary on the Vairocana Tantra (Da pi lu zhe na chengfo jingshu 大毗盧遮那成佛經疏), “According to the four directions, a viśvavajra is crafted for use as the vajra throne.”8

The vajra throne, traditionally represented as an evenly positioned viśvavajra, typically includes an eight-petal lotus depicted above it. However, the vajra throne does not seem to seamlessly integrate with the caissons. The presence of four viśvavajras inclined at a 45-degree angle cannot be construed as vajra thrones for a maṇḍala. Additionally, although twelve heavens are depicted at the four grooves, they do not fulfill central roles within the caisson maṇḍala. The author suggests that these twelve heavens may serve as ritual attendants facilitating the practice of a specific maṇḍala in a prescribed process.

Considering that the entrances of all caves in the southern area of the Mogao Caves face eastward, upon entering a single cave, individuals will face westward and have their back eastward. They stand on the ground, raise their heads, and look at the caisson just as the painters did when painting it. By doing so, the east and west orientations of the caisson are reversed, leading to the depiction as shown in the illustration (Figure 1a,b): the west slope appears on the downside of the sketch (where the east slope would typically be) while the north slope remains correctly oriented. Therefore, researchers often encounter confusion regarding the alignment of the caisson with the actual environmental directions.

In classical to medieval China, while there was no official standardization for the orientation of painting an atlas (yu-tu 與圖), two common practices prevailed: either depicting the north as upwards or the south, both reflecting the fundamental cosmic worldview of ancient Chinese culture.9 Drawing upon the imagery of the “harmony of the four symbols” (he-he-si-xiang-tu 和合四象圖) found in one of the most significant Daoist scriptures, The Guiding Principles of Ten Thousand Spirits on Dual Cultivation of Nature and Life (Xingming shuangxiu wanshen guizhi 性命雙修萬神圭旨), four mythological creatures were depicted among the Chinese constellations along the ecliptic, viewed as the guardians of the four cardinal directions. The azure dragon symbolized the east, the white tiger represented the west, the vermilion bird denoted the south, and the black warrior tortoise signified the north (refer to Figure 10). Through these representations, ancient Chinese sought to articulate the entirety of natural phenomena, a perspective that predates the introduction of Buddhism to China and extends back to the era long before the Book of Changes (Yi jing 易經).

Similarly, the maṇḍala serves as the fundamental structure of the ancient Hindu cosmic worldview. In this context, the inner directions of the maṇḍala serve as a substitute for an atlas, with each direction represented by specific colors and signs. This concept is intricately interwoven into Tantric Buddhism and is particularly evident in Yoga-Tantras from the eighth century (Tsukamoto et al. 1989, p. 188). In a standard planar Buddhist maṇḍala, as suggested by Figure 7a, the downside is typically suggesting the east in accordance with convention. The inner orientations of a single maṇḍala symbolize the arrangement of the Buddhist cosmic framework.

According to the image of “harmony of the four symbols” (Figure 10), the east is referred to as “left”, and the west as “right” when transitioning the diagram from a three-dimensional perspective (viewed from the ground to the sky) to a planar representation. According to the Books of Rites (Li ji 禮記), “Go forward, with the Vermilion Bird in the front and the Black Tortoise in the rear, the Azure Dragon to the left and the White Tiger to the right.”10

Although the east and west directions are reversed in planar context, they correspond accordingly to the orientation of the ceiling caisson. This traditional Chinese cosmological notion, prevalent during the pre-Tang era, provides insight into the process of constructing a caisson resembling a maṇḍala, as illustrated in Figure 1a.

4.2. The Maṇḍala

Differing from Zhao’s aforementioned conclusion, the author regards that each of the twelve heavens has been positioned accordingly with their proper direction. Based on the earlier studies conducted by the esteemed scholar Zhou Yiliang 周一良 (1913–2001 CE), the Sarvatathāgata Tattvasaṃgraha Tantra (Jingang ding jing 金剛頂經), which was prominently introduced by Amoghavajra 不空 (705–774 CE) in the Hexi Corridor during the Tang dynasty, is categorized within the Yoga-Tantra tradition (Zhou 1996, pp. 55–79).

Meanwhile, the most renowned homa ritual, the Homa Ritual Procedures of the Vajra Pinnacle Yoga (Jingang ding yujia humo yigui 金剛頂瑜伽護摩儀軌), stands as one of the pivotal rituals delineated in the Sarvatathāgata Tattvasaṃgraha Tantra. Homa, a fire offering ritual, holds prominence within Buddhism. The Homa Ritual mentioned above meticulously documents the procedures for creating five types of homa maṇḍalas. Among these, the śāntika maṇḍala, distinguished by a viśvavajra sign in its central part, serves as the focal point for fire offerings aimed at dispelling calamities.

As the ritual says,

… There are five kinds of fire offering kuṇḍas, all of which should be depicted as three-layered. In the central part, a viśvavajra is drawn, with lotus leaves depicted in the four corners. In the second layer, the four signs, representing the four prajñā-pāramitā bodhisattvas, are depicted, and inner offerings are made within the four corners. In the third layer, the beings from the eight directional heavens are to be depicted at the four gates and four corners. The four external offerings are also depicted while in the center, is the Vairocana. This is the composition of śāntika kuṇḍa.11

Clarifying several pivotal terms from the aforementioned excerpt, the fire offering kuṇḍa signifies the homa maṇḍala. The central yidam, the Buddha Vairocana (pi lu zhe na, 毗盧遮那), derived from the Sanskrit “vai” and “rocana”, translating to “truly shining”, corresponds to “bian zhao zun” 遍照尊in Chinese texts. The dharma body (Skt. dharmakāya) Vairocana represents the ultimate Buddha manifestation in both the Mahāvairocana Tantra and the Vajradhatu Tantra, while his enjoyment body (Skt. sambhogakāya), Rocana, serves as the central yidam and primary Buddha in The Flower Garland Sūtra (Skt. Buddhāvataṃsaka Sūtra; Chin. Da fang guang fo huayan jing 大方廣佛華嚴經) within the Chinese Esoteric Buddhist canon. The Chinese translations of bian zhao zun and “lu she na” 盧舍那 (Rocana) were commonly mixed. For instance, in Śikṣānanda 實叉難陀 (652–710 CE)’s translation of The Flower Garland Sūtra, bian zhao zun and lu she na are both used to denote Rocana (T279, No. 10, 36b12 and 82a07). In the original Tang period context of Amoghavajra, bian zhao zun could denote either Vairocana or Rocana, thus linking the two forms of the Buddha. As noted by Huang Yingjie 黃英傑, Amoghavajra translated several rituals related to Huayan’s “Dependent Origination of the Dharma-dhatu” 法界緣起. For instance, he translated The Gate of Contemplation of the Forty-Two Syllables in the Section on Entering the Dharmadhātu of the Great and Vast Buddha Flower Garland Sūtra (Da fang guang fo Huayan jing ru fajie pin si shi er zi guan men 大方廣佛華嚴經入法界品四十二字觀門) and Ritual Procedure for the Syllable-Wheel Yoga of Suddenly Realizing the Dharma-Body of Vairocana (Da fang guang fo huayan jing ru fajie pin dunzheng pi lu zhe na fashen zilun yujia yigui 大方廣佛華嚴經入法界品頓證毘盧遮那法身字輪瑜伽儀軌) (Huang 2014, pp. 291–316).

However, in all the pertinent homa-maṇḍala manuscripts from the Tang dynasty compiled by the Images of SAT Daizōkyō, the central sign of a śāntika maṇḍala is a dharma wheel rather than a viśvavajra (Figure 11). This depicts a top view of a śāntika maṇḍala. The overall structure consists of a wheel at the center, followed by a round śāntika fire kuṇḍa, with a viśvavajra throne on the outermost layer. However, it distinctly differs from the central sign. The viśvavajra throne occupies the lower and outer parts of the entire Buddhist cosmic arrangement, as depicted in a three-dimensional Yamāntaka maṇḍala from the Qing Dynasty (1644–1911 CE), preserved by the Palace Museum (Figure 12).

Another tantra attributed to Amoghavajra, titled “Scripture of the Sublime Grasp of the Immeasurable Portal” (Fo shuo chusheng wubian men tuoluoni yigui 佛說出生無邊門陀羅尼儀軌), describes the appearance of the female bodhisattva Karma-pāramitā. According to this text, it states: “Raise the palm and extend it into a five-pronged wheel. Endure it and manifest as karma, transforming into a cross-shaped viśvavajra wheel.”13 Referring to Figure 13, the samaya sign “cross-shaped wheel” of the bodhisattva Karma-pāramitā, held in her left hand, is identical to the five-pronged, cross-shaped viśvavajra.

The Homa Ritual also says, “The śāntika kuṇḍa is perfectly circular. It should be crafted as such. For the yogis’ utilizing, the śāntika kuṇḍa is crafted as a wheel.”14

Later, during the Northern Song dynasty, another prominent lo-tsā-ba (translator), Dānapāla 施護 (?–1017 CE), in his renowned Chinese-translated tantra, the Guhyasamājatantra (Fo shuo yiqie rulai jingang sanye zuishang mimi da jiaowang jing 佛說一切如來金剛三業最上秘密大教王經), mentions, ”Contemplating the grand wheel in the void, it assumes the form of a five-pronged vajra on all four sides.”15

Based on these quotations, the Chinese-translated tantras from the Tang to Song dynasties suggest that a four-sided and five-pronged viśvavajra can be contemplated as a dharma wheel. Thus, the śāntika kuṇḍa is also crafted to resemble a dharma wheel.

Returning to the caisson in Cave 361 (Figure 1a), the twelve lotus petals are structured around a circular fire offering furnace at the center. Positioned above it is a viśvavajra or dharma wheel. These two elements’ form is of a round fire offering kuṇḍa, referring to the central round part of Figure 11. Vairocana is not portrayed yet serves as both the central yidam of this microscopic Buddhist cosmic arrangement and the central deity of the entire śāntika maṇḍala, endorsing the practice.

The third layer, consisting of the ritual attendants of all homa maṇḍalas, is intricately described in the Homa Ritual.

… All beings from the eight heavens, along with signs accompany the traveler. Beginning clockwise, the eastern heaven Indra is adorned with ribbons. Agni (S1), the Heaven of fire, holds a kundikā bottle, seated on a lotus throne engulfed in flames. Yama (S) is holding a two-pronged vajra decorated with human head, and his ribbons is also likely to Indra’s. Nairrtī (W1) wields a sword, seated on a throne surrounded by flames resembling Agni. Varuṇa (W), the Heaven of Water, holds a noose with both ends resembling like vajras. Vāyu (W2), the Heaven of Wind, bears a flag and sits within a lotus flower. Vaiśravaṇa (N) brandishes a staff, ribbons alike. Īśāna (N1), with a single-end trident, radiates flames upon a lotus throne. Wise individuals should understand this truth without error.16

Transferring the caisson maṇḍala (Figure 8b) into a standard maṇḍala (Figure 8c), differences are observed. When comparing the standard maṇḍala (Figure 8c) to the aforementioned tantra, the Eastern Heaven Indra is replaced by another Eastern Heaven figure, Dhṛta-rāṣṭra (E), as found in Chinese Buddhist canons. However, an unresolved issue remains. The northeastern heaven Īśāna (N1) is the only heaven that does not align correctly in the caisson maṇḍala. In fact, it is situated in the northwest direction if referring to the standard maṇḍala sketch (Figure 8c).

Directions play a crucial role in all types of maṇḍalas, and there are two distinct systems of orientation. One is the real directions, representing the spatial arrangement of the three-dimensional caisson maṇḍala. The other is the directions depicted in the planar maṇḍala sketches used by painters to create the physical caisson maṇḍala. As discussed earlier in this article, there is a reversal of east and west when comparing the caisson (Figure 8b) to a standard maṇḍala sketch (Figure 8c). Thus, apart from the northeastern heaven Īśāna (N1), the other seven heavens in the caisson correspond to the settings of the third layer in the homa maṇḍala. However, if we rotate the three heavens of the northern groove in the caisson by 180 degrees, the maṇḍala aligns with the Homa Ritual tantra.

This mistake may have been made by the original artist during the transition from the two-dimensional sketch to the three-dimensional maṇḍala. Another caisson featuring twelve heavenly figures of the same type can be found in Cave 7. The Īśāna (N’2) is situated in the northeast direction of the northern groove (Figure 14) within the caisson. All of the aforementioned details pertain to the setup of the fire offering maṇḍala. Following this, the attracting and feeding rituals are performed,

Brahmā and Vasundhara are positioned to the right and left of Indra, with the eight directional heavens making up ten … Feeding these ten heavens … Additionally, two heavens are added among the original eight. Facing the upper heaven and the lower heaven are the sun Sūrya and the moon Candra.17

As per the ritual mentioned above, these four heavens—Brahmā (S2), Vasundhara (N2), Sūrya (E1), and Candra (E2)—are only introduced as offering attendants through the attracting and feeding rituals of the entire śāntika maṇḍala. They do not necessarily imply directional significance. Thus, the caisson is constructed in accordance with the śāntika maṇḍala introduced by the Homa Ritual Procedures of the Vajra Pinnacle Yoga.

However, upon examining the small Cave 361, there is no evidence to suggest that it was ever used for actual fire offering rituals within the cave. There are no traces of burnt residue or smudges on the murals. The Reality Assembly of the Attained Realm of the Buddhas (Zhu fo jingjie she zhenshi jing, 諸佛境界攝眞實經), translated by Master Prajñā 般若 (734 CE–?) from the Tang Dynasty, describes the practice of inner homa by contemplating the practitioner and the yidam as one:

At that time, the bodhisattva Vajrapāṇi, empowered by the Buddha’s power, expounded the true practice of inner homa for all yogic practitioners. This practice was intended to forever subdue and eliminate afflictions and all demons and spirits. In performing such homa, one should increase samādhi by visualizing one’s yidam along with the respective colors of the directions. If performing the homa for the accomplishment of the Buddha family, the yogic practitioner should deeply contemplate Vairocana Buddha and visualize oneself as Vajrasattva.18

Another lo-tsa-ba Devaśāntika 天息災 (?–1000 CE) from the Song dynasty discussed the creation of such maṇḍalas through visual meditation in his works. In his translated Chinse tantra, “The Ritual Practice of Purification Visualization and Accomplishment” (Jing xing guanxiang humo chengjiu fa pin 淨行觀想護摩成就法品) from the Mañjuśrī-mūla-kalpa (Wenshu shili genben yigui jing 文殊師利根本儀軌經), a detailed description is provided of the process of meditating on homa maṇḍalas through “chanting mantras” (T20, No. 1191, 0868a21–0869a20). Two other works by him also elaborate on “homa maṇḍala meditation”: the Great Secret Wondrous Abdhuta-Dharma Maṇḍala of All Tathāgata Tantra (Yiqie rulai da mimi wang weiceng you zuishang weimiao da mannaluo jing 一切如來大秘密王未曾有最上微妙大曼拏羅經) and Vajrasattva Tells of Vināyaka Accomplishment Ritual Tantra (Jingang saduo shuo pin na ye jia tian chengjiu yigui jing 金剛薩埵說頻那夜迦天成就儀軌經). As mentioned,

In the meditation of a homa furnace, within the vertically wide expanse of twelve fingers, establishing the seat for the central yidam. If practicing a fire offering ritual for dispelling calamities (śāntika maṇḍala) or increasing merits (pauṣṭika maṇḍala), the master should first visualize the presence of the Tathāgata Vairocana on the throne of yidam.19

Meditating on the formless fire emanating from a homa furnace internally possesses great power. Therefore, it is referred to as the inner fire offering ritual within the teachings.20

As outlined in the previously mentioned tantras, the fire offering maṇḍala can be performed through various fireless methods, including contemplation and mantra chanting. As proposed by Guo in his article, Cave 361 may have served as a venue for practicing fire offering rituals. This is indicated by the depiction of fire imagery in the Vinaya illustration in its mural, which differs from all other murals with the same subject matter in Dunhuang (Guo 2009, pp. 150–53). Through the above discussions, the primary significance of the viśvavajra appearing on the caisson ceiling is to create a śantika maṇḍala. The caisson, originally designed with the philosophical intent of preventing fire hazards, serves as the ideal location within the cave to house the intricately crafted fire offering maṇḍala. The practice of a homa maṇḍala through visual or inner meditation was a tradition that was once widely popular along the Hexi Corridor from the Tang to the Northern Song dynasty, and it even persisted into the Western Xia dynasty.

In echoing Zhao’s critique of Guo’s assumption (Zhao 2017, p. 297), the author argues against the viśvavajra sign representing Vairocana himself in this cave, particularly when surrounded by the twelve heavens. The viśvavajra of five wisdoms (五智金剛杵), clearly linked with Vairocana’s samaya, originated with the concept of “Five Wisdoms of the Buddha”. As Yin Guangming suggests, while the Four Buddhas from the slopes of Cave 361 present esoteric elements, riding on animal vehicles (Figure 1b), the first clear composition of the esoteric “Five Wisdom Buddhas” appears in the mural of Yulin Cave 35, depicted in the tenth century in the Dunhuang region (G. Yin 2014, pp. 7–20). Moreover, the four Buddhas appear at the four slopes (Figure 1b) instead of the caisson in Cave 361, making it challenging to integrate them with the central viśvavajra and twelve heavens to form a single maṇḍala. Later in this article, the author will discuss how the viśvajra began to serve as a clear samaya sign in Dunhuang around the late ninth to tenth century.

The caisson ceiling holds significant importance in every cave, serving both decorative and religious–philosophical functions. According to previous research by Zhao Xiaoxing, the Tibetans were accustomed to constructing “a stūpa” within the inner space of a cave (Zhao 2017, pp. 537–63), by painting and combining the four slopes with the west shrine. A perfect example of this is Cave 361, also designed and established by the Tibetans. In this context, the caisson ceiling is positioned above the sōrin—the summit of a stūpa, representing the uṣṇīṣa, the symbol of Buddha’s enlightenment and ultimate wisdom. Therefore, the śantika maṇḍala depicted in the caisson serves as a central maṇḍala under the tenets of Tantric Buddhist philosophy, thereby exerting the Buddhist dharma over the entire cave.

5. The Transitions from Mid-Tang to Western Xia

The caisson featuring a viśvavajra sign positioned at its center has undergone a discernible evolution through three phases across the Hexi Corridor over time.

The initial phase spans from the mid-Tang to the late Tang period (mid-ninth to late ninth century), exemplified by caves such as 7, 361 (Figure 1b), and 370, and a standardized formula was adhered to. This formula involved the depiction of a lotus encircling a round fire furnace, within which a viśvavajra sign was enclosed in the center. Four or ten directional Tathāgatas, accompanied by thousand Buddhas, were painted across the four slopes.

It is important to note that the eight or twelve heavens, conventionally associated with the four grooves, did not consistently appear in this arrangement. Rather, their presence primarily served as ritual attendants during the performance of homa rituals. This observation aligns with annotations made by the commentator Kaidou 快道 (1751–1810 CE) at the conclusion of the Homa Ritual Procedures of the Vajra Pinnacle Yoga Tantra (T18, No. 909). Kaidou suggests the possibility of two distinct textual lineages attributed to Amoghavajra, with one lineage notably omitting references to “the Eight Heavens”. These texts may vary in their level of detail or abbreviation (T18, No. 909, 0924c04–05). Hence, regardless of the presence or absence of attendant heavens, the compositional motif featuring the viśvavajra sign enclosed within a lotus-petal-encircled round furnace during the Tang dynasty could be interpreted as indicative of the śāntika maṇḍala.

The second phase began in the late Tang and lasted until the early Northern Song period (late ninth to eleventh centuries). Caissons made during this phase retained the thousand-Buddha or ten-directional Tathāgata motifs from the first phase but gradually omitted the four-directional Buddha motif on the four slopes, as seen in Caves 14 (Figure 4), 177 and 243.21 A notable example of this transition is observed in the caisson of Cave 14, where the four-directional Buddhas moved from the four slopes to the caisson, forming a complete maṇḍala with the central viśvavajra. This serves as an illustrative example of the departure from the preceding patterns seen in Cave 361.

The caisson of Cave 14 stands out as a distinctive example among all caissons featuring a viśvavajra sign. It showcases a unique configuration characterized by a 45-degree inclined, five-pronged viśvavajra positioned at the center of the square caisson, accompanied by four directional Tathāgatas. This depiction represents the first and only instance where a viśvavajra appears with such clarity, featuring five prongs. The five-pronged vajra is directly linked to the concept of the “five wisdoms” (T18, No. 885, 0473c03). This imagery serves as a metaphorical representation of “all Tathāgatas,” commonly known as the Vairocana sign (bian zhi qi 遍智契) according to interpretations found in Chinese-translated tantras (T18, No. 866, 234b24).

During the seventh century, a Tang-era Indian translator Atikūṭa 阿地瞿多 (?–?) undertook the translation of the tantra known as the Dhāraṇī Collection Scripture (Skt. Dhāraṇīsamuccaya) into Chinese, resulting in the text known as the Tuoluoni ji jing 陀羅尼集經. This was translated between 652 and 653 CE. Within this scripture, it is documented that the method involving the utilization of the sign of all Tathāgatas was for the purpose of inviting the Vajras (T18, No. 901, 0890c06). Additionally, in Vajrabodhi 金剛智 (669–741 CE)’s text Jingang ding yujia zhong lüe chu niansong jing 金剛頂瑜伽中略出念誦經 (Sūtra Abridged for Recitation), it is stated that,

At that moment, the accomplished Tathāgata Amoghasiddhi for the sake of Śākyamuni Vairocana’s sign of all Tathagatas, engages in the practice of all paramita-samayas, and has attained the Vajra Empowerment Samadhi. All these samayas are self-enlightened.22

This implies that Tathāgata Amoghasiddhi himself serves as the samaya sign and represents one of five wisdoms, namely, the karma wisdom—wisdom of all accomplishing actions, of the ultimate Tathāgata in Tantric Buddhism, Vairocana. Thus, he bears the same five-pronged viśvavajra sign as Vairocana. Furthermore, the Japanese monk Donjyaku 曇寂 (1674–1742 CE) from the Edo period (1603-1868 CE) expounded in his work Private Notes on the Vairocana Tantra (Jingang ding da jiaowang jing siji 金剛頂大教王經私記) that the all-Tathāgatas’ Samaya sign corresponds to the Chinese-translated term bian zhi qi (T61, No. 2225, 0287c23–25), signifying the sign of Vairocana’s karma wisdom and Rocana’s samaya.

In the caisson of Cave 14, the representation of the all-Tathāgatas’ sign is accompanied by the depiction of four directional Tathāgatas positioned around it. Together, these figures comprise the caisson maṇḍala. However, the configurations and mudrās of the four directional Tathāgatas were not consistent with those specified in the tantras of either the garbhakośa-dhātu or the vajra-dhātu. The four directional Tathāgatas are depicted as transitioning from their traditional locations on the four slopes of the T-truncated ceiling to the central caisson situated at the apex of the cave. This signifies a significant shift in their function within the overall composition of the cave, distinguishing it from the arrangement observed in Cave 361.

The caisson maṇḍala thus underwent a transformation, evolving from the “śāntika maṇḍala” to the “four-Tathāgata maṇḍala”, which represents an initial stage in the development toward the later commonly seen five-Tathāgata maṇḍala observed at Dunhuang. The five-pronged viśvavajra sign appearing at the caisson of Cave 14 stands as the sole example signifying the dharma body of Vairocana among all the caves, suggesting an intention to establish a prototype for the later prevalent depiction of the five-Tathāgata maṇḍala. However, a distinctive motif emerges within this evolutionary process, as the four slopes are adorned with a unique representation: three Tathāgatas accompanied by thousand Buddhas are depicted on the east, south, and north slopes, respectively, with each Tathāgata seated within a gem-encrusted tower (Figure 4).

As Amoghavajra articulated in his work Most Secret, Well-Established Dhāraṇi of the Vast, Widely Renowned, Gem-Encrusted Tower (Dabao guangbo louge shanzhu mimi tuoluoni jing 大寶廣博樓閣善住祕密陀羅尼經),

This gem-encrusted tower is square with four corners, four pillars and four doors … Now guru can open the door of this stūpa in the gem-encrusted tower. There are three Tathāgatas in this stūpa. Because of these three Tathāgatas have ultimate powers, showing the grant supernatural transformational accomplishment method. The three Tathāgatas are in this congregation.23

Returning to the caisson of Cave 14 (Figure 4), the three gem-encrusted towers positioned at the three slopes exhibit distinct iconographic characteristics reminiscent of the “four corners, four pillars, and four gates”, as described in the aforementioned tantra. Moreover, the names of the three Tathāgatas, as specified in the tantra, are Maṇi-puṣpā-dhvaja-rāja-tathāgata 摩尼寶花幢王如來, Citra-maṇi-tathāgata 種種摩尼如來, and Vajra-vikrama-abhyudgam-rāja-tathāgata 金剛超涌王如來. Three Tathāgatas are depicted convening and imparting the most esoteric Buddhist dhāraṇis. Subsequently, Śakyamuni-Tathāgata promptly ascends to the gem-encrusted tower, where he assumes a seated position alongside the three Tathāgatas.

Although partially damaged, the motif on the west slope features the sōrin of a Buddhist stūpa, accompanied by two unfolds of Buddha-attendants’ motif (Figure 15). Furthermore, Cave 14 stands out as the only central pillar cave among all those mentioned in this article to feature a caisson with a viśvavajra sign. The front half of the ceiling of the main chamber is T-truncated pyramidal, while the back half is flat (Figure 16). Within the east wall of the central pillar, there exists a stūpa-belly-like Buddhist shrine. In comparison to Cave 361, the combination of the shrine and the west slope forms a construction reminiscent of a Buddhist stūpa (Figure 16).

This shrine houses a statue of Śakyamuni in the ground-touched mudrā posture, established during the Qing dynasty, along with statues of six arhats. Additionally, the shrine features depictions of the ten disciples painted on the south, west, and north walls. Adjacent to each disciple, there is a rectangular banner, one of which is inscribed with the name “the first one, Vinaya monk Upāli” 優婆離持律第一, who is among the “ten principal disciples” of the Buddha. Altogether, sixteen Buddhas are depicted within the Buddhist shrine: fifteen seated Buddhas are painted at the top of the shrine walls, with Śakyamuni positioned inside the shrine. This motif appears to correspond with the “The Analogy of Transformed City” (Hua cheng yu pin 化城喻品) in The Wonderful Dharma Lotus Sūtra (Miaofa lianhua jing 妙法蓮華經), which records the names of the sixteen Buddhas from the ten directions, respectively,

Those sixteen śrāmaṇeras, disciples of Buddha, have now all attained Anuttarā Samyaksaṃbodhi. In various worlds of the ten directions, they are presently teaching the Dharma, accompanied by innumerable hundreds of thousands of millions of bodhisattvas and śrāvakas as their attendants. Two of these śrāmaṇeras became Buddhas in the east: one named Akṣobhya in the Land of Joy, and the other named Merukūṭa. In the southeast, there are two Buddhas: one named Siṃhaghoṣa and the other named Siṃhadhvaja. In the south, there are two Buddhas: one named Ākāśapratiṣṭhita and the other named Nityaparinirvṛta. In the southwest, there are two Buddhas: one named Indradhvaja and the other named Brahmadhvaja. In the west, there are two Buddhas: one named Amitābha and the other named Sarvalōkadhātupadravodvega-pratyuttīrṇa. In the northwest, there are two Buddhas: one named Tamālapatra-candana-gandhâbhijña and the other named Merukalpa. In the north, there are two Buddhas: one named Meghasvaradīpa and the other named Meghasvararāja. In the northeast, there is one Buddha named Sarvalokādīptabhayamanyita-vidhvaṃsanakara. The sixteenth one is myself, Buddha Śākyamuni.24

According to Guo’s research on this shrine, the depiction of the fifteen (sixteen) Buddhas symbolizes all Tathāgatas of the ten directions and three times (Guo 2006, pp. 143–74). Beneath the central pillar, there are three donor inscriptions, each revealing the names of the donors: Liu Niangzi (the sixth wife) from the He family 六娘子賀氏, daughter Adun Xili 妮子阿敦悉力, and daughter Yanmei 妮子延美 (Dunhuang Academy 1986, p. 8). It is conceivable that this cave was established by two daughters as an act of offering merits and virtues for their late mother. Their mother, Liu Niangzi from the He family, was also recorded in an inscription found in Mogao Cave 9 when she was married (Dunhuang Academy 1986, p. 6). In the two daughters’ Chinese names, Adun is a Uyghur name, while Yanmei appears to be derived from a common Tibetan name, “Ye-med”, which means “nothingness”.25 Therefore, it is plausible that the donors were either Tibetans or part of a Tibetan–Uyghur family.

The absent fourth Buddha, Śakyamuni, materializes within a stūpa formed by a grand shrine with a west slope, reminiscent of the formation found in the western part of Cave 361. As he ascends to his tower, accompanied by the three-tathāgata motifs adorning the slopes from the east, south, and north, a harmonious convergence unfolds. This synthesis creates a vivid tableau, illustrating the Tathāgata imparting the mysteries of Buddhist tantras.

However, the murals from Cave 14 are more esoteric than those from Cave 361. The caisson, housing the maṇḍala of the four directional Tathāgatas, is intricately positioned at the top of the esoteric Buddhist stūpa, with the sign of “all Tathāgatas’ samaya”, a five-pronged viśvavajra, at its center.

The third phase, spanning from the early Northern Song to the Western Xia dynasty (eleventh to thirteenth centuries), marks an evolution in caisson composition style. During this period, the caisson maṇḍala typically feature a viśvavajra positioned at the center of a round fire furnace (or an absence of a fire furnace) solely, within a square caisson. This design is accompanied by obscure elements such as the “circular floral pattern” painted (or sometimes absent) on the four slopes. This style omits the depiction of ritual attendant heavens and the directional Tathāgatas or thousand Buddhas, as observed in examples like Caves 30, 87 (Figure 5), 140, 291, 326, 328, and 382 from the Western Xia dynasty.26 Under this phase, the depiction of the eight or twelve heavens, the four or ten directional Tathāgatas, and the thousand-Buddha motifs were no longer deemed essential to the suggesting caisson maṇḍala. Instead, the viśvavajra sign emerged as a definitive and metaphorical sign on certain caisson ceilings.

Dating back to the Liao dynasty (907–1125 CE), paralleling to the early Northern Song to the Western Xia dynasty, the figure of Rocana underwent a transformation into the esoteric Buddha Vairocana, as evidenced by numerous illustrations found on the title pages of the Chinese Buddhist canon, The Flower Garland Sūtra, printed during the Liao to Western Xia dynasty. This contribution was pioneered by a Huayan monk in the Liao dynasty, Jue Yuan 覺苑 (1034 CE–?). His work Explanation of the Meanings of the Vairocana-abhisaṃbodhi-tantra (Da pi lu zhe na chengfo shenbian jiachi jing yi shi yan mi chao, 大毗盧遮那成佛神變加持經義釋演密鈔) masterfully integrated Huayan teachings with Esoteric Buddhism, synthesizing elements from the works of Cheng Guan 澄觀 (737–838 CE), the fourth patriarch of the Huayan School, specifically his Commentaries and Sub-commentaries on the Avataṃsaka Sūtra (Huayan jing shu chao, 華嚴經疏鈔), along with Yi Xing’s Commentary on the Vairocana-Tantra. This early amalgamation, as detailed by Huang, marked a pioneering step in bridging Huayan philosophy with Esoteric Buddhist principles within the Buddhist textual tradition (Huang 2014, pp. 291–316).

This amalgamation was largely prevalent in the Hexi Corridor during the Western Xia dynasty. The wood-block Buddhist illustrations of The Flower Garland Sūtra produced during the Western Xia dynasty, the principal figure of Rocana in Chinese Buddhist context, was transformed into “the hierarch Maha-Vairocana” (jiaozhu da pi lu zhe na fo 教主大毗卢遮那佛), with his name written inside a rectangular banner above his head (Figure 17). This change, combined with the Chinese esoteric Buddhist doctrine from the Vairocana Sūtra,27 highlights Rocana representing the Sambhogakaya and Vairocana representing the Dharmakaya. Rocana evolved into a more tantric figure, depicted with the fist of wisdom mudrā in illustrations, aligning with the mudrā of Vairocana as seen in the Tibetan Anuttara-yoga Tantra. Thus, the two hierarchs are unified as one, sharing the same samaya sign under Sino-Tibetan Tantric Buddhist traditions.

Until the late Tang period at the end of the ninth century, the significance of the five-pronged viśvavajra sign began to symbolize “all-Tathāgatas,” persisting into the early Northern Song period. The final amalgamation of the esoteric and exoteric Buddhas was elucidated by the Liao monk and soon appeared in illustrations from Western Xia. The central yidam Vairocana in all fire offering rituals from the Vajra-dhatu Tantra gradually merged in significance with the samaya of his Sambhogakaya Rocana from Huayan, or Maha-Vairocana from the Vairocana Sūtra.

6. Conclusions

The viśvavajra serves dual roles as both a ritual object and a Tantric Buddhist sign. While the viśvavajra stands out as a distinctive sign representing a specific maṇḍala, its meanings vary depending on its placement within the maṇḍala.

From both a constructional design and Buddhist doctrinal perspective, the caisson ceiling holds paramount importance within each individual cave. Serving as a manifestation of Buddhist maṇḍalas, these specific caissons occupy a central position in the cave’s philosophical framework, emphasizing their profound significance.

When the viśvavajra is positioned at the center of the caisson ceiling, its original composition and significance, featuring a round fire furnace from the mid-Tang period, align with the concept of a homa maṇḍala, particularly the śāntika maṇḍala. This maṇḍala and its associated fire-offering rite were not commonly practiced in a literal sense, as the caisson itself was designed with the philosophical intent of preventing fire hazards. According to the tantras, the central deity of every homa maṇḍala is Vairocana, envisioned through visual meditation above the basic painted planar maṇḍala. In the image and context of the śāntika maṇḍala, the viśvavajra sign is regarded as equivalent to a dharma cakra.

As the caisson evolved to feature the five-pronged viśvavajra sign at its center, accompanied by the four directional Tathāgatas, it began to serve as a preliminary representation of the five-Buddha motif. This shift in design and significance marked a transition towards representing the “all-Tathāgata’s samaya” of both Vairocana and Rocana. The sign transformed into a definitive Buddhist metaphor and a vital fusion of the two hierarchs from Sino-Tibetan Tantric Buddhist traditions, a significance that began to emerge around the tenth century and persisted into the thirteenth century. The ritual attendants of the śāntika maṇḍala depicted on the caisson, along with the directional Tathāgatas and thousand-Buddha motifs on the four slopes, lost their significance in composing a śāntika-maṇḍala ceiling within the Mogao Caves. Multiple layers of meaning converged, unified under the samaya sign of Vairocana.