Thailand is notorious for its range of arcane festivals. But one of the strangest is the tattoo honouring ceremony held each March at Wat Bang Phra temple about 50 miles west of Bangkok near the town of Nakhon Chai SiPhotograph: Andrew SpoonerLike Phuket's Vegetarian Festival, with its mass piercings, and the Bun Bang Fai rocket festival, where thousands of fireworks explode into the sky in a giant fertility rite, it is linked to Thailand's spiritual domainPhotograph: Andrew SpoonerWat Bang Phra's former abbot Luang Phor Phoem, who died a couple of years ago, was famous for creating particularly powerful sak yant (tattoos) and attracted thousands of committed devotees. The monks of the temple continue the tradition using a single thin needle about 18 inches longPhotograph: Andrew SpoonerIn Thai culture the sak yant is often worn as a symbol of spiritual and physical protection and they mostly display a mixture of cabalistic spells in ancient Khmer/Cambodian script or animals such as tigers and monkeys Photograph: Andrew SpoonerDuring the festival devotees who have been tattooed return to the temple to have their tattoos re-empowered by the monks in a large puja (festival) that attracts a couple of thousand peoplePhotograph: Andrew SpoonerThe crowds usually begin to congregate shortly after sunrise with the thick heat of the Thai summer (March and April) enveloping the gatheringPhotograph: Andrew SpoonerIt is a deeply spiritual festival, with intoxication of any form completely forbidden and the seated monks and devotees who attend can often be glimpsed in deep meditationPhotograph: Andrew SpoonerSome will sit shirtless proudly displaying large elaborate tattoos. At first, a sense of ordered calm pervades the festival. Many devotees will fall into a trance-like statePhotograph: Andrew SpoonerThis serenity doesn't last long. Eerie cries begin to ring out from within the crowd and a few of the devotees begin to contort their faces and bodies Photograph: Andrew SpoonerThey leap to their feet, clench fists and let out long screams, clawing at the ground and air. It is a frightening and bizarre spectacle to a Westerner but many Thais will sit giggling or remain indifferentPhotograph: Andrew SpoonerThe devotees are in fact undergoing what they believe to be a form of possession by the animal spirits inculcated into their tattoos. Some are very clearly monkeysPhotograph: Andrew SpoonerOthers are tigers and buffalos. During the possession some will seemingly become enraged, attempting to charge the plinth where the senior monks are delivering the spritual prayersPhotograph: Andrew SpoonerConveniently for the leaping tigers or crouching monkeys, the crowd has already formed into neat patterns with runs cleared for possessed devotees to sprint towards the plinthPhotograph: Andrew SpoonerThere is an air of order amid all the wild screams and roars, with drink sellers and noodle stalls nearby should you need respite. Families with children attend - for some Thais it is an engaging day outPhotograph: Andrew SpoonerTo break the spell of possession the devotee must be lifted into the air and have their ears rubbedPhotograph: Andrew SpoonerFor this very purpose a platoon of soldiers is drafted in to protect the senior monks sitting on the plinth. Suitably calmed, the devotee immediately wanders oblivious back into the crowdPhotograph: Andrew SpoonerIn the past it was common for almost all Thais to be tattooed. These days many still have discreet protective sak yant placed above the hairline on the nape of the neck or use transparent sesame oil to create an invisible marking. But the tattoos from Wat Bang Phra temple are believed to have magical powers protecting against knives and gunsPhotograph: Andrew SpoonerMost tattoo devotees are men in 'dangerous' professions. These can include policemen and soldiers through to labourers, motorcycle taxi drivers and, of course, members of Thailand's notorious criminal underworldPhotograph: Andrew SpoonerThe festival ends when the monks spray holy water on to the crowd. In the minutes leading up to this, the possessions are at their most intense and can happen in large numbers. The water spraying comes as a relief in the burning heat and the crowd quickly disperses afterwards, the devotees placated for another yearPhotograph: Andrew SpoonerThis year's festival takes place on Saturday 7 March. The date is usually the Saturday nearest the last full moon before the April Thai New Year (Songkran).