He led the development in Venice of the elaborately-framed polytych or "composite altarpiece" form, which became popular all over Italy during the 13th century, partly in response to liturgical changes (only reversed in the 20th century) which placed the priest celebrating mass on the same side of the altar as the congregation, so with his back to them for much of the time. This encouraged the creation of altarpieces behind and above the altar, as a visual devotional focus. He is thwe oldest Venetian painter whose name is known, and the earliest to paint the new subject of the Coronation of the Virgin.