Dome

Architectural element, cornice detail; It was erected to commemorate Constantine I's victory over Maxentius at the Battle of Milvian Bridge on October 28, 312. Dedicated in 315, it is the latest of the existing triumphal arches in Rome, from which it differs by spolia, the extensive re-use of parts of earlier buildings. The arch is heavily decorated with parts of older monuments, which assume a new meaning in the context of the Constantinian building. Another explanation given for the re-use is the short time between the start of construction (late 312 at the earliest) and the dedication (summer 315). Source: Wikipedia; http://en.wikipedia.org/wiki/Main_Page (accessed 7/16/2010)