Basilica of Saint-Denys, Argenteuil

The relic is a brownish garment of wool, dyed with madder, surviving as fragments mounted on a backing; it is venerated as the seamless tunic that John's Gospel says Jesus wore to the crucifixion, the robe "woven in one piece from the top" for which the soldiers cast lots so as not to tear it. Because the Gospel stresses that it was without seam, the tunic became a powerful symbol of the unity of the Church.

The Argenteuil cloth has been examined several times: studies in the twentieth and twenty-first centuries reported bloodstains, pollen said to be consistent with the Near East, and weaving of an ancient type, while a radiocarbon test in 2004 returned a date around the seventh century, which supporters attribute to contamination or to the many times the fabric was handled, cut and repaired. The Church venerates it as a relic of the Passion without asserting its scientific authenticity. The garment is fragile, which is one reason it is kept sealed and shown only at long intervals rather than displayed continuously.

The Argenteuil tradition holds that the tunic came west as an imperial gift: the Byzantine empress Irene is said to have sent it to Charlemagne, who around the year 800 gave it to his daughter Theodrade, a nun and later abbess at Argenteuil. During the Viking raids on the Seine the nuns reportedly walled the relic up for safety, and it was found again by the monks of the priory of Saint-Denys around 1156, after which its record at Argenteuil is continuous. Its most dramatic escape came during the French Revolution, when the parish priest Ozet, fearing the relic would be seized and destroyed, cut the tunic into several pieces and hid them separately; after the Terror the surviving fragments were recovered and sewn back together, which accounts for the garment's present patched state. The current basilica of Saint-Denys, a neo-Romanesque church, was built between 1862 and 1866 specifically to shelter the tunic and to accommodate the crowds who come to venerate it.

Two churches in western Europe claim to hold the seamless robe of Christ: the basilica of Saint-Denys at Argenteuil and the cathedral of Trier in Germany, which keeps the Holy Coat (Heiliger Rock). The two relics are physically different objects with separate histories, and rather than treat them as rivals the Church has generally regarded them as distinct venerated garments associated with the Passion, leaving the historical question open.

Argenteuil shows its tunic only at exceptional ostensions decided by the bishop, traditionally about once every fifty years but in practice at irregular intervals, notable modern showings took place in 1934, 1984, 2016 and again in 2025, the last drawing crowds estimated in the hundreds of thousands over several weeks. Between ostensions the relic is kept locked in a reliquary and is not on view, which preserves both its fragile fabric and the sense of occasion around each rare display. The basilica is an active parish church of the Diocese of Pontoise.