The Image of Edessa, known in Greek as the Mandylion, was one of the most venerated relics of the Byzantine world: a cloth said to carry the face of Christ imprinted without human painting, the archetype of the acheiropoieta. Its fame rested on the legend of Abgar, the toparch of Edessa in Mesopotamia, who was believed to have written to Jesus asking for healing and to have received in return a miraculous portrait. As the model "true likeness," the image did much to fix the bearded, frontal type of Christ that became standard in icons. Unlike most relics in this collection, the Mandylion is no longer extant: it can be traced with confidence only as far as its disappearance during the sack of Constantinople in 1204, after which its fate is unknown, making it a lost object known chiefly through texts and through the icons it inspired.
Tradition holds that King Abgar of Edessa, gravely ill, wrote to Jesus asking him to come and heal him, and that Jesus sent back either a letter or, in the fuller later version of the legend, a cloth bearing a miraculously imprinted image of his face, the Mandylion, which cured the king. The legend is first attested, in its earlier letter-only form, by the fourth-century church historian Eusebius of Caesarea, with the miraculous image itself appearing in the surviving textual tradition considerably later, a documented development of the story over time rather than a single fixed account from its earliest attestation.