Archaeologists have found the complete remains of a 2,500 year-old residence near Rome's central train station that suggests the ancient city was actually much larger than originally believed.

The rectangular house was unearthed during the excavation of an area near Termini station, reported AKI.

Archaeologists say it is one of the most important discoveries in the capital in recent years.

"The remains of this house from the beginning of the sixth century BC is an almost unparalleled example of ancient architecture in this city," said Francesco Prosperetti, superintendent for Rome's Archaeological Heritage.

The dwelling is intact, with wooden beams and clay-covered walls and a roof, as well as archaeological clues point to domestic use of the building.

The house may have been custodian's residence linked to a nearby temple from around the same period that was discovered in 2013.

"This is an exceptional find, among the most important of the last 10 years," Prosperetti said.

Mirella Serlorenzi, the excavation chief said the find showed the populated area of Rome was not just around the Roman Forum in the sixth century BC as previously thought.

"At the beginning of the sixth century BC, Rome was much larger than we previously thought before this latest discovery," Serlorenzi said.

Archaeologists previously believed that in ancient times the Qurinal Hill was used as a sacred area, with temples and a necropolis.

The Qurinal Hill now hosts the Italian president's official residence and before that the king of Italy, as well as the pope.