The Duomo di Montepulciano was begun in 1592 and completed in the eighteenth century, leaving the facade in bare brick — it was never given the stone cladding originally intended, giving the cathedral a slightly unfinished appearance that distinguishes it from its neighbours on Piazza Grande. The interior, however, is more rewarding than the exterior suggests.
The cathedral's principal treasure is the Assumption triptych by Taddeo di Bartolo, a masterpiece of early fifteenth-century Sienese painting that originally stood on the high altar. The predella panels are particularly fine. The cathedral also contains fragments of the Arazo monument by Michelozzo and a baptismal font decorated with della Robbia-style reliefs.