The monastery walls, 732 meters long and 7 meters thick, were constructed in 1654-80. They incorporate parts of the earlier citadel, which helped to withstand the Polish siege in 1612. The first construction works were supervised by Jean de Gron, a French military engineer known in Russian sources as Anton Granovsky. After the monastic authorities denigrated his Western-style design as alien to Russian traditions, Granovsky was replaced by a team of native masters. The fortress was the largest erected in Muscovy after the Time of Troubles; its walls feature numerous towers, each built to a particular design. The most remarkable are the Chasuble, the Tent-like, the Vologda, and the Smithy towers.