Today, Aquileia is a town smaller than the colony first founded by Rome. Over the centuries, sieges, earthquakes, floods, and pillaging of the ancient buildings for materials means that no edifices of the Roman period remain above ground. The site of Aquileia, believed to be the largest Roman city yet to be excavated, is inscribed on the UNESCO World Heritage List.
Excavations, however, have revealed some of the layout of the Roman town such as a segment of a street, the north-west angle of the town walls, the river port, and the former locations of baths, of an amphitheater, of a Circus, of a cemetery, of the Via Sacra, of the forum, and of a market. The National Archaeological Museum contains over 2,000 inscriptions, statues and other antiquities, mosaics, as well as glasses of local production and a numismatics collection.
The most striking remains of the Roman city are those of the port installations, a long row of warehouses and quays that stretch along the bank of the river. These were incorporated into the 4th century defences, substantial traces of which can be seen today.
The Arch of Constantine is situated between the Colosseum and the Palatine Hill. It was erected by the Roman Senate to commemorate Constantine I's victory over Maxentius at the Battle of Milvian Bridge in 312. Dedicated in 315, it is the largest Roman triumphal arch. The arch spans the Via triumphalis, the way taken by the emperors when they entered the city in triumph.
Though dedicated to Constantine, much of the decorative material incorporated earlier work from the time of the emperors Trajan (98-117), Hadrian (117-138) and Marcus Aurelius (161-180), and is thus a collage. The last of the existing triumphal arches in Rome, it is also the only one to make extensive use of spolia, reusing several major reliefs from 2nd century imperial monuments, which give a striking and famous stylistic contrast to the sculpture newly created for the arch.
The arch is 21 m high, 25.9 m wide and 7.4 m deep. Above the archways is placed the attic, composed of brickwork reveted (faced) with marble. A staircase within the arch is entered from a door at some height from the ground, on the west side, facing the Palatine Hill. The general design with a main part structured by detached columns and an attic with the main inscription above is modelled after the example of the Arch of Septimius Severus on the Roman Forum.