 The first renovations occurred under Pope Leo IV (847-855), who built the crypt under the nave, added to side aisles, enclosed the courtyard before the facade, and built the belltower and the chapels of Saints Barbara and Nicholas.The new remarkable basilica, Carolingian architecture in style, was 95 m long and 50 m wide.This church, however, was burned to the ground by Robert Guiscard's troops during the Norman Sack of Rome (1084).