A new baptistery (S Giovanni) was set into the slope beneath to support the new choir construction. In 1319, probably under the direction of Camaino di Crescentino ( fl 1298-1338), the walls and piers of the baptistery were built on the foundations, and in 1320 marble was being brought for the external facing. In 1325 the great arches over the baptistery to support the new choir bays were completed. Shortly afterwards, work on the baptistery and choir extension was suspended, and it was resumed only after the failure of the Duomo Nuovo. From 1355 a 'veritable army' (Lusini) of workmen was engaged to complete the work, recruited by Domenico d'Agostino ( fl 1343-1369), Master of the Works until c. 1369. The portals of the baptistery are based on a drawing datable to the 1320s (Siena, Mus. Opera Duomo), but three large windows were built instead of the four projected in the drawing. The polychrome marble facade was given a horizontal roof line, but the top section, at the level of the cathedral clerestory, was left in rough stone, and in 1369 the large oculus made for the end of the old choir was transferred to it.