I consider one of my greatest accomplishments on this blog to be discovering the origin of Sun Wukong’s golden headband. This would not have been possible without reading about the Hevajra Tantra (8th-century) in Robert Nelson Linrothe’s (1999) Ruthless Compassion: Wrathful Deities in Early Indo-Tibetan Esoteric Buddhist Art. This amazing study analyzes Esoteric Buddhist statues and texts to trace the evolution of these guardians from mere dwarf attendants to mighty warrior gods endowed with the power of the Five Wisdom Buddhas. This is a great resource for anyone researching religious art involving wrathful guardians in Buddhism, Daoism, and of course Chinese folk religion, for the iconography of these divine warriors spread far and wide.
I am sharing a PDF of the book found on libgen for the benefit of other scholars. The black and white portions of the book appear to be based on a xeroxed copy. However, there are full color plates in the back.
Buddhists believe that the wrathful spirits represent inherent qualities of our own, and that meditating on them can transmute the otherwise malevolent sides of our own natures into positive qualities and actions. The wrathful deities also provide precious clues as to the early development of esoteric Buddhism in India, about which few early texts survive. Through careful examination of a large body of images as well as Sanskrit, Tibetan, and Indic texts, this lavishly illustrated volume traces the evolution of the forms and the unfolding significance of the wrathful deity in esoteric Buddhist sculpture.
Sun Wukong‘s golden headband (jingu, 金箍; a.k.a. jingu, 緊箍, lit: “tight fillet”) (fig. 1) is an instantly recognizable part of his popular iconography. Anyone who’s read Journey to the West (Xiyouji, 西遊記, 1592 CE) will know that it painfully tightens around our hero’s skull to correct any unsavory behavior. “What kind of behavior?” someone might ask. Well, mass murder, of course! In chapter 56, for example, Monkey’s Buddhist master Tripitaka recites the spell to punish him for beating a group of bandits to death with his magic staff and beheading one of them with a blade (Wu & Yu, 2012, vol. 3, p. 89).
Fig. 1 – A modern replica of Monkey’s golden headband (larger version).
This spell is first revealed to the monk by Guanyin in chapter 14:
I have a spell which is called the True Words for Controlling the Mind [dingxin zhenyan, 定心真言], or the Tight-Fillet Spell [jingu er zhou, 緊箍兒咒]. You must memorize it secretly; commit it firmly to your memory, and don’t let anyone learn of it […] When [Sun Wukong] returns, give him…the cap [containing the headband] to wear; and if he again refuses to obey you, recite the spell silently. He will not dare do violence or leave you again” (Wu & Yu, 2012, p. 317).
You can see the exact words are never revealed. This is not surprising, though, as the spell is one of the few things in the entire Buddho-Daoist cosmos that can control Sun Wukong. Tripitaka’s life would be in danger and the journey would be doomed if any villains got ahold of this secret. But … what if … we could guess the spell, just for fun? I’d like to suggest a mantra based on historical religious beliefs and iconography. This thought experiment was written for the benefit of artists and fanfiction writers looking to create more accurate portrayals of the novel and its characters.
I. The Band’s Religious Background
As I note in this article, the golden fillet is based on a ritual headband worn by Buddhist ascetics in ancient India. The Hevajra Tantra (Dabei kongzhi jingang dajiao wang yigui jing, 大悲空智金剛大教王儀軌經, 8th-c.) states yogins must wear the band and a list of other prescribed ritual items in their worship of the wrathful protector deity Heruka (Linrothe, 1999, p. 250). Most importantly, the tantra states the band symbolizes the Buddha Akshobhya (Ch: Achu, 阿閦; Budong, 不動; lit: “Immovable”) (fig. 2), who gained enlightenment through moralistic practices of right speech and action (Linrothe, 1999, p. 251; Buswell & Lopez, 2013, p. 27).
Fig. 2 – A depiction of Akshobhya (larger version).  Artist unknown.
Akshobhya and the other esoteric Wisdom Buddhas are sometimes depicted as small figures or colored jewels in the headdress of the Manjusri Bodhisattva (and other Buddhist personages) (Getty, 1914/1988, p. 37; Vessantara, 1993, p. 155). Akshobhya is symbolized by the color blue (Getty, 1914/1988, p. 36). A cursory Google image search shows the blue jewel is often set in the top most position over Manjusri’s forehead (fig. 3).
This might suggest a more religiously accurate version of Sun Wukong’s golden headband would include a figure or jewel representing Akshobhya.
Given the above information, I’d like to suggest the tightening spell for Monkey’s headband—within the context of our thought experiment—is the Akshobhya Mantra! There are two kinds. I’ll leave it up to you which one you like best. The first is a short recitation of the buddha’s name: Oṃ a kṣo bhya hūṃ (fig. 4). This can be very roughly translated as “Praise to the Immovable One!”. Om and Hum are both holy syllables invoking spiritual power and enlightenment, respectively. They also appear in the more well-known Oṃ maṇi padme hūṃ (Ch: An mo ni ba mi hong, 唵嘛呢叭咪吽). One Chinese version of the name mantra appears to be “An a bie zha zhi ga hong hong” (唵 阿別炸枝嘎 吽吽).
The second is a longer chant, again called the “Mantra of Akshobhya” (Achu fo xinzhou, 阿閦佛心咒) (fig. 5 and video 1). It’s interesting to note that the historical Xuanzang (on whom Tripitaka is based) is known to have translated a version of this mantra. 
Reciting this to rein in Sun Wukong not only references the band’s historical and religious connection to Akshobhya but also serves as a physical reminder of right speech and action (how the deity gained buddhahood). It’s Tripitaka’s way of screaming, “Stop murdering everyone within arm’s reach!”
Fig. 6 – Shifu Pigsy (a.k.a. Zhu Bajie) reciting “Amituofo” to activate the golden headband on the Monkey Prince, son of the original Monkey King (larger version). From Yang, 2021, p. 80. Copyright DC Comics.
The case for Akshobhya’s mantra being the tight-fillet spell is strengthened—again, within the context of our thought experiment—by the fact that he has power over strong negative emotions. According to Bangdel and Huntington (2003): “The transcendental insight represented by Akshobhya is mirrorlike wisdom (adarsha jnana), which…is the antidote to the poison of anger, or hatred” (p. 91). The monk Tripitaka assuages these emotions by activating the golden headband, once again reminding Wukong of right speech and action.
In addition, Akshobhya and Gautama have matching iconography: both are shown seated with the left hand palm up on the lap and the right reaching down to touch the earth. Hinayana Buddhists of Sri Lanka and Southeast Asia worship Gautama in this form, but Mahayana worships Akshobhya as such (see note #1). This is important as Gautama gives the three golden headbands to Guanyin in order to pacify any demons that she might encounter during her search for the scripture pilgrim (Wu & Yu, 2012, vol. 1, pp. 206-207). This shows there is a connection between the two Buddhas, and it also explains why Gautama would gift a headband associated with Akshobhya.
Various online sources and adaptations sometimes refer to the spell as the “Headache Sutra” (for example). But to my knowledge it’s never explicitly called this in the novel. The pain associated with the spell is generally used as a threat. For example, in chapter 16, Tripitaka exclaims: “Monkey! Aren’t you afraid of your headache [ni toutong, 你頭痛]? Do you still want to behave badly? (Wu & Yu, 2012, vol. 1, p. 347) (emphasis mine).
Chapter 25 provides two more names for the spell:
There is, moreover, the Tight-Fillet Spell or the Tight-Fillet Sutra [jingu er jing, 緊箍兒經]. It’s also [Tripitaka’s] “Old Saying Sutra” [jiuhua er jing, 舊話兒經].  The moment he recites that, I’ll have a terrible headache, for it’s the magic trick designed to give me a hard time (Wu & Yu, 2012, vol. 1, p. 468).
I’ve written an article that explains the origins of the “crescent-style” headband.
[He] is represented seated, like all the Dhyani-Buddhas, with the legs locked and both feet apparent. There are often wheels marked on the soles of his feet, or a protuberance like a button, resembling the urna on the forehead. His left hand lies on his lap in ‘meditation’ mudra. His right touches the earth with the tips of the outstretched fingers, the palm turned inward. This is called the bhumisparsa or ‘witness’ mudra.
The Hinayana Buddhists in Ceylon, Java, Burma, and Siam worship Gautama Buddha under this form, while those of the Mahayana school look upon it as Akshobhya; for, with but rare exceptions, the historic Buddha is only appealed to by the Northern Buddhists in his ethereal form of Amitabha.
Akshobhya may also take in Tibet another form of Gautama Buddha called ‘Vajrasana’ (diamond throne). The attitude is the same as the above, but before him on the lotus throne lies a vajra, or it may be balanced in the palm of the left hand lying in ‘meditation’ mudra on his lap (Getty, 1914/1988, p. 36).
2) The Chinese source refers to Akshobhya as the “Immovable Buddha” (Budong rulai, 不動如來).
3) I’ve added an extra sentence from the Chinese original glossed over in the translation. Yu (Wu & Yu, 2012) translates the spell as the “Old-Time Sutra” in a previous sentence (vol. 1, p. 468).
Bangdel, D., & Huntington, J. C. (2003). The Circle of Bliss: Buddhist Meditational Art. United Kingdom: Serindia Publications.
Buswell, R. E., & Lopez, D. S. (2013). The Princeton Dictionary of Buddhism. Princeton, NJ: Princeton University Press.
Getty, A. (1988). The Gods of Northern Buddhism: Their History, Iconography and Progressive Evolution through the Northern Buddhist Countries. New York: Dover Publications, Inc. (Original work published 1914)
Linrothe, R. N. (1999). Ruthless Compassion: Wrathful Deities in Early Indo-Tibetan Esoteric Buddhist Art. Boston, Mass: Shambhala.
Vessantara. (1993). Meeting the Buddhas: A Guide to Buddhas, Bodhisattvas, and Tantric Deities. United Kingdom: Windhorse Publications.
Wu, C., & Yu, A. C. (2012). The Journey to the West (Vols. 1-4) (Rev. ed.). Chicago, Illinois: University of Chicago Press.
The golden headband or fillet (jingu, 金箍; a.k.a. jingu, 緊箍, lit: “tight fillet”) is one of the Monkey King’s most recognizable iconographic elements appearing in visual media based on the great Chinese classic Journey to the West (Xiyouji, 西遊記, 1592 CE). It is generally portrayed as a ringlet of gold with blunt ends that meet in the middle of the forehead and curl upwards like scowling eyebrows (type one) (fig. 1). A different version is a single band adorned with an upturned crescent shape in the center (type two) (fig. 2). Another still is a simple band devoid of decoration (type three) (fig. 3). Sun first earns the headband as punishment for killing six thieves shortly after being released from his five hundred-year-long imprisonment. The circlet is a heaven-sent magic treasure designed to reign in the immortal’s unruly, rebellious nature. Since Sun Wukong is a personification of the Buddhist concept of the “Monkey of the Mind” (xinyuan, 心猿), or the disquieted mind that bars humanity from enlightenment, the fillet serves as a not so subtle reminder of Buddhist restraint. Few scholars have attempted to analyze the treasure’s history. In this paper I present textual and visual evidence from India, China, and Japan that suggests it is ultimately based on a ritual headband worn by Esoteric Buddhist Yogin ascetics in 8th-century CE India. I also show how such fillets became the emblem of some weapon-bearing protector deities in China, as well as military monks in Chinese opera.
1. The Headband’s Literary Origin and Purpose
The headband is first mentioned in chapter eight when three such “tightening fillets” are given to the Bodhisattva Guanyin by the Buddha in order to conquer any demons that she may come across while searching for a monk who will bring sutras back to China from India:
“These treasures are called the tightening fillets, and though they are all alike, their uses are not the same. I have a separate spell for each of them: the Golden, the Constrictive, and the Prohibitive Spell. If you encounter on the way any monster who possesses great magic powers, you must persuade him to learn to be good and to follow the scripture pilgrim as his disciple. If he is disobedient, this fillet may be put on his head, and it will strike root the moment it comes into contact with the flesh. Recite the particular spell which belongs to the fillet and it will cause the head to swell and ache so painfully that he will think his brains are bursting. That will persuade him to come within our fold” (Wu & Yu, 2012, vol. 1, pp. 206-207).
Guanyin later explains in volume two which demons get which fillet (Wu & Yu, 2012, vol. 2, p. 251).
Sun Wukong earns the “Constrictive” (jin, 緊) band in chapter fourteen after brutally murdering six thieves who accost his master Tripitaka, the chosen scripture seeker, on the road to the west. The killings cause the two to part ways, and it is during Monkey’s absence when Guanyin gives the monk a brocade hat containing the fillet and teaches him the “True Words for Controlling the Mind, or the Tight-Fillet Spell” (喚做『定心真言』，又名做『緊箍兒咒』) (Wu & Yu, 2012, vol. 1, p. 317). Sun is eventually persuaded to return and tricked into wearing the hat under the guise of gaining the ability to recite scripture without rote memorization. It soon takes root, and the powerful immortal is brought under control through the application of pain. He then promises to behave and to protect Tripitaka during their long journey to the Western Paradise. 
The remaining two fillets are used by Guanyin to conquer other monsters in later chapters. She throws the “Prohibitive” (jin, 禁) band onto the head of the Black Bear Demon (Hei xiong jing, 黑熊精) in chapter seventeen and, after reciting the spell, he agrees to become the rear entrance guard of her Potalaka Island paradise (Wu & Yu, 2012, vol. 1, p. 365). The “Golden” (jin, 金) band is split into five rings—one each for the head, wrists, and ankles—and used to subdue Red Boy (Hong hai’er, 紅孩兒), the fire-spewing son of the Bull Demon King and Princess Iron Fan, at the end of chapter forty-two and the beginning of forty-three (Wu & Yu, 2012, vol. 2, pp. 251-252). The child demon becomes her disciple and eventually takes the religious name “Sudhana.” 
Monkey is forced to wear the fillet until he attains Buddhahood in chapter one hundred, causing it to vanish (Wu & Yu, 2012, vol. 4, p. 383). The band’s disappearance at the end of the novel denotes Sun’s internalization of self-control. But the treasure doesn’t disappear forever. It appears once more in the Later Journey to the West (Hou Xiyouji, 後西游記, 17th-century CE), a sequel set 200 years after the original. The story follows a similar trajectory with Monkey’s descendant Sun Luzhen (孫履真, “Monkey who Walks Reality”) attaining immortality and causing havoc in heaven. But this time the macaque Buddha is called in to quell the demon. Monkey quickly disarms the “Small Sage Equaling Heaven” of his iron staff and pacifies him not with trickery but with an enlightening Buddhist koan. He then places the band on Luzhen’s head to teach him restraint (see Liu, 1994).
It appears very few scholars writing in English have attempted to trace the origins of the golden fillet. Wang Tuancheng theorizes that the idea for the headband came from two sources. First, the historical journal of Xuanzang (602-664 CE), the Tang Dynasty monk on whom Tripitaka is loosely based, details how he was challenged to a religious debate by a man in a foreign kingdom who offered his own head as the price of defeat. Xuanzang won, but instead of collecting his prize, the monk took the man as his servant. Second, Wang notes that slaves during the Han Dynasty (206 BCE-220 CE) wore a metal collar around their neck shaped like the Chinese character for twenty (nian, 廿). He goes on to explain: “…the author transformed the metal hoop that the non-Buddhist might have worn to Sun Wukong’s headband” (Wang, 2006, p. 67).
I’m not particularly persuaded by this argument since Wang doesn’t offer any evidence as to why a Han-era slave implement would still be in use during the Tang (618-907 CE) four to five hundred years later; nor does he suggest a reason for why such a collar would be moved from the neck to the head. Besides, there exists religious art featuring the fillet (see below) that predates the novel by centuries, meaning it wasn’t the sole invention of the author-compiler of the novel.
Before I continue, I would like to point out that the 13th-century CE precursor of the novel, The Story of How Tripitaka of the Great Tang Procures the Scriptures, does not mention the fillet at all (this is just one of many differences between it and the final 16th-century CE version). Monkey is simply portrayed as a concerned individual who purposely seeks out Tripitaka to ensure his safety, as the monk’s two previous incarnations have perished on the journey to India. In other words, he comes as a willing participant, which negates the need for positive punishment via the ringlet.  But at least two pictorial representations of Monkey coinciding with the Song Dynasty (960-1279 CE) depict him wearing a band, which, again, excludes the treasure being a later invention.
In her excellent paper on the origins of Sun Wukong, Hera S. Walker (1998) discusses a 13th-century CE stone relief from the western pagoda of the Kaiyuan Temple (開元寺) in Quanzhou, Fujian province, China that portrays a sword-wielding, monkey-headed warrior (pp. 69-70). Considered by many to be an early depiction of Monkey, the figure wears a robe, a Buddhist rosary, and, most importantly, a type one fillet on the forehead (Fig. 4).  Walker quotes Victor Mair, who believes the fillet “recalls the band around the head of representations of Andira, the simian guardian of Avalokitesvara” (the Indian counterpart to Guanyin) (Walker, 1998, p. 70). He goes on to list similarities between the stone relief and depictions of Andira, while also suggesting said depictions are based on south and southeast Asian representations of the Hindu monkey god Hanuman:
Identical earrings (these are key iconographic features of H[anuman] in many Southeast Asian R[ama saga]s), comparable tilt of the head… which seems to indicate enforced submission, long locks of hair… flaring out behind the head, elongated monkey’s mouth, similar decorations on the forearm and upper arm, etc. It is crucial to note that all these features can be found in South Asian and Southeast Asian representations of H[anuman] (Walker, 1998, p. 70).
So as it stands, the 13th-century CE appears to be the furthest that the motif has been reliably traced.
Fig. 4 – The 13th-century CE stone relief of Sun Wukong from the Kaiyuan Temple in Quanzhou, Fujian province, China (larger version).
3. My Findings
While Mair suggests a Southeast Asian Hindo-Buddhist influence, I know of at least one example from northeastern China that suggests an Indo-Tibetan Buddhist influence. The Eastern Thousand Buddha Cave no. 2 (Dong qianfo dong di 2 ku, 東千佛洞第2窟) in the Hexi Corridor of Gansu Province contains a late-Xixia dynasty (late-12th to early-13th-century CE) mural of Xuanzang worshiping Guanyin from a riverbank. Monkey stands behind him tending to a brown horse. He is portrayed with a type three circlet on his head, waist length hair, and light blue-green robes with brown pants (fig. 5). This painting was completed during a time when China was seeing an influx of monks fleeing the inevitable fall of India’s Buddhist-led Pala Dynasty (750-1174 CE) from the 10th to the 12th-century CE. They brought with them the highly influential Pala Buddhist art style and Vajrayana Buddhism, a form of esoteric Buddhism. The MET (2010) writes:
A mixture of Chinese-style and Vajrayana traditions and imagery was employed in the Tangut Xixia Kingdom … which was based in Ningxia, Gansu, and parts of Shanxi … It is difficult to imagine that this “new” type of Buddhism, which not only was flourishing in Tibet in the late tenth century but was also found in the neighboring Xixia Kingdom and may have been practiced by Tibetans based in the Hexi Corridor region of Gansu Province, was completely unknown in central China until the advent of the Mongols (p. 19).
The painting of Monkey and Tripitaka was surely created by an Indian/Tibetan Buddhist monk (or at the very least a fellow Tangut/Chinese practitioner) living in the area. This suggests that the imagery within the painting, such as the fillet, could have an Esoteric Buddhist pedigree, and textual evidence shows such headbands were indeed worn in some esoteric rituals.
The yogin must wear the sacred ear-rings, and the circlet on his head (emphasis added); on his wrists the bracelets, and the girdle round his waist, rings around his ankles, bangles round his arms; he wears the bone-necklace and for his dress a tiger-skin… (Linrothe, 1999, p. 250).
Furthermore, it describes how each of the ritual adornments and implements used in the ceremony represents each of the five esoteric Buddhas, as well as other religio-philosophical elements:
Aksobhya is symbolized by the circlet (emphasis added), Amitabha by the ear-rings, Ratnesa by the necklace, and Vairocana (by the rings) upon the wrists. Amogha is symbolized by the girdle. Wisdom by the khatvanga [staff] and Means by the drum, while the yogin represents the Wrathful One himself [i.e. Heruka]. Song symbolizes mantra, dance symbolizes meditation, and so singing and dancing the yogin always acts (Linrothe, 1999, p. 251).
As can be seen, the circlet represents Aksobhya (Sk: “Immovable”; Ch: Achu, 阿閦; Budong, 不動). This deity is known for his adamantine vow to attain buddhahood through the practice of Sila, or “morality”, the aim of which “is to restrain nonvirtuous deeds of body and speech, often in conjunction with the keeping of precepts” (Buswell & Lopez, 2014, pp. 27 and 821). So the ritual band most likely served as a physical reminder of right speech and action, making it the best candidate for the origin of Monkey’s fillet. Sun is after all the representation of the “Monkey of the Mind” (as noted in the introduction), so his inclusion in the Eastern Thousand Buddha Cave painting was probably meant to convey the taming of this Buddhist concept via the circlet (apart from referencing the popular tale itself).
The Hevajra Tantra, the textin which the circlet appears, was first translated into Tibetan by Drogmi (993-1074 CE) and adopted during the 11th-century CE as a central text by the respective founders of the Kagyu and Sakya sects, two of the six major schools of Tibetan Buddhism. Various members of the Sakya sect were invited by Mongol royalty to initiate them into the text’s esoteric teachings during the 13th-century CE. These include Sakya Pandita and his nephew Chogyal Phagpa, who respectively tutored Genghis Khan‘s grandson Prince Goden in 1244 and Kublai Khan in 1253. The meeting between Kublai and Chogyal resulted in Vajrayana Buddhism becoming the state religion of Mongolia. The Hevajra Tantrawas translated into Chinese by the Indian monk Dharmapala (963-1058 CE) in 1055 during the Northern Song Dynasty (960-1127 CE). The text, however, did not become popular within the Chinese Buddhist community like it would with the Mongols in the 13th-century CE (Bangdel & Huntington, 2003, p. 455). But this evidence shows how the concept of the 8th-century CE ritual circlet could have traveled from India to East Asia to influence depictions of Sun Wukong in the 11th-century CE. And the relatively unknown status of the text in China might ultimately explain why there are so very few depictions of Chinese deities wearing the fillet, or why it does not appear in the 13th-century CE version of Journey to the West.
While the late-Xixia mural (fig. 5) lacks many of the ritual adornments (apart from the fillet) mentioned in the Hevajra Tantra, the Quanzhou stone relief (fig. 3) includes the band, earrings, necklace, bangles, and possibly even a tiger skin apron, suggesting it too has an esoteric origin (most likely based on Chinese source material).  The band’s connection to esoteric Buddhism is further strengthened by a 12th-century CE painting from Japan. Titled Aka-Fudo (赤不動), or “Red Fudo [Myoo],” it depicts the wrathful esoteric god seated in a kingly fashion, holding a fiery, serpent-wrapped Vajra sword in one hand and a lasso in the other (fig. 6). He wears a golden, three-linked headband (similar to the curls of type one), which stands out against his deep red body and flaming aureola. Biswas (2010) notes: “…the headband on his forehead … indicate[s], according to some, a relation to the habit of groups of ascetics who were among the strong supporters of Acalanatha” (p. 112). His supporters were no doubt yogin practitioners in the same vein as those who worshipped Heraku and other such wrathful protector deities.
Fig. 5 – A portion of the late-Xixia (late-12th to early-13th-century CE mural) in the Eastern Thousand Buddha Cave number two (larger version). Fig. 6 – The 12th-century CE Japanese painting “Aka-Fudo” (赤不動) (larger version).
3.1. The Fillet as a Symbol of Martial Deities and Warrior Monks
It’s important to note that Monkey was not the only cultural hero of the Ming Dynasty (1368-1644 CE) to wear a golden fillet. Another example is Li Tieguai (李鐵拐), or “Iron Crutch Li,” the oldest of the Eight Immortals.  Li is generally portrayed as a crippled beggar leaning on a cane. Legend has it that his original body was cremated prematurely by a disciple while the immortal traveled in spirit to answer a summons from Lord Laozi, the high god of Daoism. Li’s spirit returned a day later to find only ashes, thus forcing him to inhabit the body of a recently deceased cripple. According to Allen and Philips (2012), “Laozi gave him in recompense a golden headband and the crutch that was to become his symbol” (p. 108). Some depictions of Li wearing the fillet predate Journey to the West. The most striking example is Huang Ji’s Sharpening a Sword (early-15th-century CE) (Fig. 7), which portrays the immortal wearing a type three band and sharpening a double-edged blade on a stone while staring menacingly at the viewer.  One theory suggests Li’s martial visage identifies him as a “spirit-guardian of the [Ming] state” (Little, 2000, p. 333). Both Monkey and Li are therefore portrayed as brutish, weapon-bearing, golden headband-wearing immortals who serve as protectors. This shows the fillet was associated with certain warrior deities during the Ming.
The fillet’s connection to religion and martial attributes culminated in the Jiegu (戒箍, “ring to forget desires”), a type two band worn by Military Monks (Wuseng, 武僧) in Chinese opera to show that they have taken a vow of abstinence (fig. 8). Such monks are depicted as wearing a Jiegu over long hair (Bonds, 2008, pp. 177-178 and 328), which contrasts with the bald heads of religious monks.  I would like to suggest that the band’s half-moon shape may have some connection to a Ming-era woodblock print motif in which martial monks are shown wielding staves tipped with a crescent (fig. 9)(Note: see my 07-25-22 update for the foreign origins of this motif). The exact reason for the shape is still unknown (Shahar, 2008, pp. 97-98), but the association between the crescent and martial monks seems obvious. The use of the fillet in Chinese opera led to it being worn by Sun Wukong in the highly popular 1986 live-action tv show adaptation of the novel (fig. 2). 
Examples of past research into the origins of the golden fillet respectively point to a slave collar from the Han dynasty (206 BCE-220 CE) and circa 13th-century CE South and Southeast Asian depictions of the Buddhist guardian Andira and the Hindu monkey god Hanuman as possible precursors. However, the first isn’t credible, and the second, while on the right track, doesn’t go back far enough. A late-12th to early-13th-century CE mural in the Eastern Thousand Buddha Cave complex depicts Sun Wukong wearing a type three fillet with possible ties to a ritual circlet worn by Esoteric Buddhist Yogin ascetics in 8th-century CE India. The Hevajra Tantra, the esoteric text that mentions the band, associates it with the Aksobhya Buddha and thereby his moralistic, self-restraining practices. The text was transmitted from India to Tibet, China, and Mongolia from the 11th to the 13th-centuries CE, showing a clear path for such imagery to appear in East Asia. A 12th-century CE Japanese Buddhist painting of the guardian deity Fudo Myoo with a fillet suggests that the practice of wearing circlets in esoteric rituals continued for centuries. Other non-Buddhist deities became associated with the fillet during the Ming Dynasty. A 15th-century CE painting of the immortal Li Tieguai, for example, depicts him as a type one circlet-wearing, sword-wielding guardian of the Ming dynasty. All of this suggests that the band became a symbol of weapon-bearing protector deities. The association between the fillet and religion and martial attributes led to its use as the symbol of military monks in Chinese opera.
I’ve been wondering what the 8th-century CE version of the circlet (along with the other ritual implements) mentioned in the Hevajra Tantra might have looked like. While I have yet to find a contemporary sculpture or painting, I have found an 11th to 12th-century CE interpretation from Tibet. Titled The Buddhist Deity Hevajra (fig. 10), this copper alloy statue somewhat follows the prescribed iconography of the god as laid out in the aforementioned text:
Dark blue and like the sun in colour with reddened and extended eyes, his yellow hair twisted upwards, and adorned with the five symbolic adornments,/ the circlet, the ear-rings and necklace, the bracelets and belt. These five symbols are well known for the purificatory power of the Five Buddhas./ He has the form of a sixteen-year-old youth and is clad in a tiger-skin. His gaze is wrathful. In his left hand he holds a vajra-skull, and a khatvahga [staff] likewise in his left, while in his right is a vajra of [a] dark hue…(Linrothe, 1999, p. 256)
The circlet here is depicted as a fitted band with crescent trim and a teardrop-shaped adornment (a conch?) (fig. 11). The statue’s iconography more closely follows that from the Sadhanamala (“Garland of Methods”), a compilation of esoteric texts from the 5th to 11th-centuries CE. The following information probably derives from the later part of this period:
He wields the vajra in the right hand and from his left shoulder hangs the Khatvanga [staff] with a flowing banner, like a sacred thread. He carries in his left hand the kapala [skull cap] full of blood. His necklace is beautified by a chain of half-a-hundred severed heads. His face is slightly distorted with bare fangs and blood-shot eyes. His brown hair rises upwards and forms into a crown which bears the effigy of Aksobhya. He wears a kundala [ear decoration] and is decked in ornaments of bones. His head is beautified by five skulls (Donaldson, 2001, p. 221).
Our statue has many of these features but lacks the image of the Buddha in his hair. This suggests the knob visible in the coif (fig. 10) once carried such a figure. So once again we see the importance of the Aksobhya Buddha. The statue is similar to 10th and 11th-century CE stone statues from India. 
While this doesn’t get us any closer to what the original circlet looked like, this statue adds to the mutability of the fillet imagery. The Hevajra Tantra is vague in its description, and so it is no surprise that so many variations have appeared over the centuries. The original sanskrit text uses the word cakri (circle) to refer to the band (Farrow & Menon, 2001, pp. 61-62). This might explain the simple type three fillet worn by Monkey in the Eastern Thousand Buddha Cave two painting (fig. 2).
I have written an article suggesting an origin for the type one headband, or as I now call it, the “curlicue headband.”
One thing I figured out a while ago but never explained here was the reason why the Japanese Buddhist protector deity Aka-Fudo (赤不動) (fig. 6) is depicted with a headband. I believe this is a visual representation of the fillet’s association with the Aksobhya Buddha. This is because the fudo (Ch: budong, 不動) of Aka-Fudo and the Sanskrit meaning of Aksobhya respectively mean “immovable.” So the image of Aka-Fudo is encapsulating both his position as a protector deity and the Buddha represented by the headband.
I’ve written an article suggesting a mantra for the secret spell that causes the golden fillet to tighten.
Little, S. (2000). Taoism and the Arts of China. Chicago, IL: Art Institute of Chicago.
Liu, X. (1994). The Odyssey of the Buddhist Mind: The Allegory of the Later Journey to the West. Lanham, Md: University Press of America.
Metropolitan Museum of Art, Leidy, D. P., Strahan, D. K., & Becker, L. (2010). Wisdom Embodied: Chinese Buddhist and Daoist sculpture in the Metropolitan Museum of Art. New York: Metropolitan Museum of Art.
Shahar, M. (2008). The Shaolin Monastery: History, Religion, and the Chinese Martial Arts. University of Hawaii Press.
Walker, H.S. (1998). Indigenous or Foreign? A Look at the Origins of Monkey Hero Sun Wukong. Sino-Platonic Papers, 81, 1-117.
Wang, T. (2006). Dust in the Wind: Retracing Dharma Master Xuanzang’s Western Pilgrimage. Taipei: Rhythms Monthly.