BBC News' Orla Guerin on a rich find in the heart of Rome

Archaeologists have called the discovery 'sensational' and believe there may be many more treasures lying undiscovered in the area.

One expert said the site, which is in the heart of the city under the ancient Trajan Baths, could be Rome's Pompeii, the ancient Italian city which was buried under a volcanic eruption.

Surprise findings

Earlier this year, a first century fresco was discovered on the same site, depicting a colourful bird's eye view of a city that experts believe may be ancient Rome. The fresco is now being painstakingly restored.

Work in the area began as a low key clean-up, and archaeologists say that nobody was expecting such important discoveries.

The deeper they dig - the more they find

Archaelogist Andrew Wallace-Hadrill says fresco goes down 8m

The latest find is a mosaic which is two metres high and a metre wide, and depicts a man leaning on a column. City officials said it appears to be part of a large, decorated wall, believed to date from around the end of the second century.

A tiny camera lowered into the excavation site showed another, even larger mosaic nearby showing a man harvesting grapes.