Only this church in the centre of the square remains from the famous Benedictine monastery of St Martin. Built in 1066 with large yet finely detailed stone blocks, this church marks an important stage in Romanesque architecture in Castile. Following experiments in Palencia, Jaca and the Basilica of San Isidoro in León, it achieved perfection in its architectural arrangement. The church underwent extensive restoration work in 1904 which has given it a somewhat austere appearance.