To the west of the Museo Archeológico in Siena, near the town walls, stands the Church of San Doménico, a severe brick building in Cistercian Gothic style. Originally built in 1226, it was subsequently much altered and enlarged; the battlemented campanile, in a style alien to Cistercian architecture, was erected in 1340. The church has an aisleless nave with an enclosed rectangular choir and a surprisingly high and spacious transept, from which the two chapels flanking the choir are entered. The effect of the interior is mainly due to its lack of decoration, which enhances the impression of space. In the northwest transverse wall of the nave is the entrance to a vaulted chapel with the earliest known likeness of St Catherine of Siena (1347-80), a fresco by Andrea Vanni (c. 1400).