one of the first Italian painters to break with the centuries-old conventions of Byzantine painting, such as rigid compositional balance and frontality. Although the precise dating of his work has not been established, it is clear that he introduced more spontaneous gestures and scenes of human tenderness to 13th-century Italian painting, helping to make possible the later acceptance in Italy of emotive Gothic painting.

The only work attributed to Guido by all authorities is a large painting of the “Virgin and Child Enthroned,” once in the Church of San Domenico at Siena and later moved to the Palazzo Pubblico. It bears a rhymed Latin inscription, giving the painter's name as “Gu . . . o de Senis,” with the date 1221. Certain critics argue on stylistic grounds that it must have been painted between 1262 and 1286 and that the date found on the altarpiece was forged when it was overpainted at the turn of the 14th century. Most agree, however, that the early date is original, making Guido far in advance of other Italian painters of his time. A “St. Dominic” (Fogg Art Museum, Cambridge, Mass.), “St. Peter Enthroned,” and “Madonna and Four Saints” (both in the Pinacoteca Nazionale, Siena) have also been attributed to him.