The church, with its centralized planning and Roman character, broke decisively with Spanish traditions of ecclesiastical design. Through the narthex is a public chapel, a centralized area situated beneath the monks’ choir and covered by a remarkable flat sail vault, with a floor-plan that repeats the main and private body of the basilica, but on a much smaller scale. The church is organized as a Greek cross within a square, and this main area was inspired by Michelangelo’s St Peter’s Basilica, but with the original apses squared in the manner of Alessi’s S Maria Assunta in Carignano, Genoa. The cupola of the latter had a direct influence on that of the Escorial, which was the first in Spain to be built with a drum. The main arms of the cross have barrel vaults, the corner areas have sail vaults, and a high gallery runs around the inner perimeter.