Taken March 7/09 Rome, Italy

The Arch of Constantine (Italian: Arco di Costantino) is a triumphal arch in Rome, situated between the Colosseum and the Palatine Hill. 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 21 m high, 25.7 m wide and 7.4 m deep. It has three archways, and the lower part of the monument is built of marble blocks, the top (called attic) is brickwork reveted with marble.
The arch spans the Via Triumphalis, the way taken by the emperors when they entered the city in triumph. This route started at the Campus Martius, led through the Circus Maximus and around the Palatine Hill; immediately after the Arch of Constantine, the procession would turn left at the Meta Sudans and march along the Via Sacra to the Forum Romanum and on to the Capitoline Hill, passing both the Arches of Titus and Septimius Severus.
The arch is heavily decorated with parts of older monuments, which assume a new meaning in the context of the Constantinian building. As it celebrates the victory of Constantine, the new “historic” friezes illustrating his campaign in Italy convey the central meaning: the praise of the emperor, both in battle and in his civilian duties. The other imagery supports this purpose: decoration taken from the “golden times” of the Empire under Trajan, Hadrian and Marcus Aurelius places Constantine next to these “good emperors”, and the content of the pieces evokes images of the victorious and pious ruler.
The main inscription would originally have been of bronze letters. It can still be read easily; only the recesses in which the letters sat, and their attachment holes, remain. It reads thus, identically on both sides:

IMP · CAES · FL · CONSTANTINO · MAXIMO · P · F · AVGUSTO · S · P · Q · R · QVOD · INSTINCTV · DIVINITATIS · MENTIS · MAGNITVDINE · CVM · EXERCITV · SVO · TAM · DE · TYRANNO · QVAM · DE · OMNI · EIVS · FACTIONE · VNO · TEMPORE · IVSTIS · REM-PVBLICAM · VLTVS · EST · ARMIS · ARCVM · TRIVMPHIS · INSIGNEM · DICAVITTo the Emperor Caesar Flavius Constantinus, the greatest, pious, and blessed Augustus: because he, inspired by the divine, and by the greatness of his mind, has delivered the state from the tyrant and all of his followers at the same time, with his army and just force of arms, the Senate and People of Rome have dedicated this arch, decorated with triumphs.

(Courtesy Wikipedia)