Lorenzo Monaco, The Martyrdom of Pope Caius

Tempera on panel
The J. Paul Getty Museum, Los Angeles

The executioner returns his bloodied sword to its scabbard after beheading St. Caius. Diocletian's order that Caius be killed is reflected in his pointing gesture. In the background, only one person notices that angels are lifting the saint to Heaven in a mandorla.

Some of the sources cited in the Acta Sanctorum (April vol. III, 14-17) speak of Caius as a martyr, some as a "confessor" – that is, a person who professed the Christian faith but was not martyred. But the official Roman Martyrology and Roman Breviary for April 22 state unequivocally that he was "crowned with martyrdom under Prince Diocletian."

In Monaco's painting he is decapitated, a notion that arises from the fact that his brother Gavinius (or Gabinus) and his niece Susanna were said to have been martyred by the sword. In Vivarini's Polyptych of the Body of Christ Caius is one of the four beheaded martyrs who flank the image of the Man of Sorrows.

The same sources also claim that Diocletian was a relative of the two brothers, who like him were from Dalmatia. The artist has reflected this claim by making Diocletian and Caius resemble each other.

The form of Caius's papal tiara – a single cone with a jeweled band around the bottom – had gone out of use at the beginning of the century.

View this image in full resolution.

Photographed at the site by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.