"This is an historiated capital O, an initial in the The San Domenico Missal. Fra Angelico made the illustrations in that missal while working in the convent of San Domenico in Fiesole, near Florence.
Depicted is the moment Jesus calls the fishermen Peter and Andrew. The shoreline and the lake that vanish into the horizon behind them help to create a strong suggestion of depth in this tiny picture."
Art created c. 1430