EARLY Rome was not as we imagine it. It was a “shimmering city on water” and — like Venice — subject to frequent flooding, according to a leading American archaeologist.

Professor Albert Ammerman, who was educated in Britain and is known for his work on the archaeology of Venice as well as the origins of the Roman Forum, says that he has established that the Tiber “was not where it is today. It was a much broader river, stretching to the foot of Capitol Hill. This means that we have to completely rethink our idea of early Rome”.

Professor Ammerman’s discovery shows that “a traveller approaching Rome in the Republican era — say at the time of the Punic Wars — would have seen an astonishing sight: the Temple of Jupiter towering above him on Capitol Hill, but also a line of other great temples on the river bank, appearing to rise out of the water.”

The remains of the riverside temples are now marooned in a busy thoroughfare 100 yards back from the present Tiber embankment, “and we tend to assume that that was pretty much the case in ancient times too. But, in fact, the river was where the road now is, right under Capitol Hill,” he says.

Professor Ammerman, who studied environmental archaeology at London University and now teaches at Colgate University in New York, obtained the consent of the Rome city council to drill 24 “cores” or bore holes in and near the Velabrum Valley, which lies between the Capitoline and Palatine Hills and leads to the Forum.

“The material extracted shows us that there was a man-made riverbank much further inland from the present Tiber,” he says. “There is a structure of cappellacio tufa blocks used in the sixth century followed by grotta oscura, another kind of volcanic rock which we know the Romans brought from the Etruscan city of Veii and used for building after they conquered it in 396BC.” This dating has been confirmed by experts from Oxford University.

Ammerman says that until now scholars have underestimated “the dynamic nature of the Tiber, the extent to which it rises and falls. Since the modern embankment was built in the late 19th century the river has been channelled. But in fact it can go from three metres above sea level to between eleven and thirteen metres. This means it would have flooded the Velabrum regularly, creating an effect in Rome not unlike the acqua alta of Venice.”

Ammerman says this explains why the Temple of Vesta, the Temple of Portunus, the god of harbours, and temples to Janus, Hope and Juno — now incorporated into the 12th-century Church of San Nicola in Carcere — were built on podiums some 15 metres high.

By contrast the “Archaic Temple” from the 6th-century BC, the remains of which lie in the Velabrum between a 1930s office block and the 15th-century Church of Sant’ Omobono (St Homobonus), was only 7m above sea level. Both the temple and the riverside plaza in front of it — the site of a busy “emporium” trading in salt and other goods — “must have flooded quite often”.

Ammerman says there was also a “misconception” about the Velabrum itself, which on most maps was shown as having been a “swamp”.

“Obviously it was wet some of the year, but it dried out. Our drilling revealed a firm clay bed with man-made gravel walkways across it. I believe this is where Rome’s roof tiles were made, beginning in the sixth century BC, when they were an innovation. It was a kind of industrial area in the heart of the city.”

Under his Italian assistant, Dunia Filippi, Ammerman’s team may also have solved one of the the great remaining mysteries of ancient Rome: the site of the long-lost Temple of the Deified Augustus, erected after the death of Augustus, the first Emperor, who was hailed as a god.

The team found a massive travertine platform with a cemented basalt foundation 11-metre deep, by drilling in the courtyard of the present Rome police headquarters.

“It could be the Temple of Minerva, which has never been found either, but my money is on the Temple of Augustus,” he says. “It’s certainly the mother of all temple foundations.”

Despite his vision of Rome as a “city on water”, Professor Ammerman says that scholars may have to rethink a long- held theory that the port of the city of Rome lay between Tiber Island and the ruined Aemilian Bridge (now known as the Ponto Rotto, or Broken Bridge).

Although there is evidence of Roman warehouses in the area, both the bridge and the island would have made it “almost impossible for boats to get in and out”, he says. He says that the port was probably further down-river, beneath the Aventine Hill.