It was built where the old town of Acqui Terme is to be found; it is reached through a fine Renaissance-style square, laid out towards the end of the 15th century. Originally consecrated in 1067, over the years it has undergone numerous rebuilding and renovation works but the original parts of the building can be seen in the transept and the presbytery, in the lantern window and in the mullioned windows in the lower part of the bell tower. In the facade, a twin-columned 17th century atrium frames the superb entranceway in marble which was completed in 1481 by Giovanni Antonio Pilacorte; the lunette has a bas relief dedicated to the Assumption of the Virgin. The interior, with five naves, in notable for the size of the three Romanesque-style apses which have been extremely well preserved. Underneath the transept is the cruciform crypt. Of interest are the cloisters next to the church, dating from 1495, with a doorway and loggia featuring bas reliefs from the period. The sacristy is home to a precious triptych, the Vergine di Montserrat, by the important Spanish painter Bermejo.