Oct. 2, 2009 -- Beneath Rome's Fiumicino airport lies a "mini-Colosseum" that may have played host to Roman emperors, according to British archaeologists.

The foundations of the amphitheater, which are oval-shaped like the much larger arena in the heart of Rome, have been unearthed at the site of Portus, a 2nd century A.D. harbor near Ostia's port on the Tiber River.

A monumental seaport that saved imperial Rome from starvation, Portus is now reduced to a large hexagonal pond on a marshy land owned by a noble family, the Duke Sforza Cesarinis.

The two-square-mile site has been known since around the 16th century, but only in the 1860s was it seriously excavated by the Italian archaeologist Rodolfo Lanciani, who marked the remains of what he believed was a theater.

Another finding, a 295-foot (90-meter) shipping canal, further confirmed the importance of Portus.

Begun by the emperor Claudius in 42 A.D., inaugurated by Nero and greatly enlarged by Trajan in the 2nd century A.D., the harbor fed a city of more than 1 million down into the Byzantine period and beyond.

Ships from Egypt, Turkey, Greece and the Middle East unloaded supplies into 300-meter-long warehouses supported by 15-meter brick arches.