Saint Peter Martyr or Saint Peter of Verona was a 13th century Catholic priest and celebrated preacher. According to legend, he was killed by two Cathar assassins, who struck his head with an axe. Before he died, Peter offered his blood as a sacrifice to God, dipping his fingers in it and writing on the ground ‘Credo in Unum Deum’. Here Saint Peter is shown full-length, standing on blue clouds against a gold background. He is wearing a black and white Dominican habit and his gory head wound is clearly visible, framed by a golden halo. He holds a martyr's palm in his right hand and a large red book in his left hand. Fra Angelico had himself entered the Dominican order. He joined the house in S. Domingo, Fiesole at an unknown date and after a period in Rome returned to Fiesole as its Prior c. 1449. From about 1438-45 he was the artist most favoured by the Medici, and is known to have employed many assistants. Fra Angelico frequently worked on Dominican altarpieces, and it is likely that this panel originally belonged to a series set into a flanking pilaster of an altarpiece-frame, although others like it have yet to be identified.