Romanesque architecture developed between 800-1100 AD and was characterized by thick walls, small windows, round arches, and barrel or groin vaulting. Churches during this period served to spread Christianity and featured a Latin cross plan with a nave, aisles, transept, and apse. Sculptural decoration appeared on church portals and capitals. The Pisa Cathedral complex, built between 1063-1118, exemplifies Romanesque architecture with its large nave and aisles, projecting transept and crossing dome, and famous leaning bell tower.