Sienese painter, pupil of Ambrogio Lorenzetti. His best two fresco cycles are at S. Gimignano, one dealing with Old Testament subjects in the Collegiata (1356) and one in the church of S. Agostino on the birth and death of the Virgin (1366). He was the most successful Sienese painter of the later fourteenth century. He shared a workshop with Andrea Vanni, and produced a large number of altarpieces and frescoes, and, in addition, collaborated with other artists on mural and altarpiece paintings and polychrome sculptures. He worked on many of his most important commissions with his son, Andrea di Bartolo. //