Marshall said the sculpture was probably commissioned by a rich individual who could afford to have it made in a different part of England. The eagle, a typical Roman symbol, represents good while the serpent epitomizes evil, he said.
The eagle is currently owned by Scottish Widows Investment Partnership Property Trust and its development partners Endurance Land.
Once an archeological treasure is found, it is placed in the care of MOLA, which analyzes and conserves it and publishes a report on the discovery. In most cases, the landlord then donates the object to a museum or archive, which in London is usually the Museum of London.
The eagle is considered priceless, according to MOLA.
Earlier this year, separate digs on the site of Bloomberg LP's future London headquarters revealed Roman building remains and some 10,000 well-preserved objects that led the site to be dubbed the "Pompeii of the north."
Museum of London archeologists discovered good-luck charms, coins, drains and even leather shoes dating from the mid-40's A.D., when the Romans founded London, to A.D. 410. The objects were in good condition because a now-lost river, the Walbrook, kept the ground wet and prevented their decay.
Bloomberg LP is the parent company of Bloomberg News.
The eagle is on display for six months at the Museum of London: www.museumoflondon.org.uk.