Italian archaeologists have found the remains of a barracks that they believe was used by ancient Rome's equivalent of the secret service.
The discovery was made during deep excavations for a new metro station in Rome, named Amba Aradam after a mountain plain in Ethiopia where Italian forces fought a pitched battle in 1936 during the Abyssinian War.
The main part of the 2nd century barracks was discovered in 2016, but new areas have now been uncovered, including the home and office of a centurion who would have commanded a militia.
"The building could have been one of those that accommodated special militias, who were the secret service of the emperor," said senior archaeologist Rossella Rea.
The remains of the building were found at a depth of around 38ft beneath street level.
It boasted a dozen or so rooms arranged around a courtyard with a fountain.
Archeologists also discovered well-preserved mosaic floors depicting cupids, dancing satyrs, olive trees and ornamental fountains, as well as the remains of flights of steps and a room with under-floor heating.
Next to the “domus” or house were the remains of another structure, probably a warehouse for storing food and other goods.
The barracks, which include a dormitory for legionaries, were part of a huge imperial military complex that was built during the reign of the Emperor Hadrian.
The complex included cavalry barracks, which now lie beneath the Basilica of St John Lateran, one of the capital’s largest churches.
The Amba Aradam station is part of Rome’s third metro line, which is still under construction.
“The route of the new metro line has turned out to be an astounding archeological site,” said Francesco Prosperetti, Rome’s superintendent of archeology.
“There’s been a series of discoveries of great significance, some of the most important found in Rome in recent years.”
Archeologists also found a number of artefacts, including a carved ivory handle from a dagger, amulets and gold rings.
The mosaics and artefacts are to be carefully removed, cleaned and installed in the new metro station, which is due to be finished in 2022.
“One thing is certain – this will be the most beautiful underground metro station in the world,” said Mr Prosperetti.
The site is around half a mile from the Colosseum, the ancient gladiatorial arena.
The barracks were abandoned and built over when high protective walls were built around the city by the Emperor Aurelian in the late third century AD.
Amba Aradam will be one of two new metro stations displaying archaeological finds.
They ranged from iron spearheads and gold coins decorated with emperors’ heads to a delicate perfume bottle made from turquoise glass and marble statues of scantily-clad nymphs.
As passengers descend the station’s stairways, they will travel back in time, from the Middle Ages to Imperial Rome and right back to Republican Rome.
The fact that engineers had to dig down so deep in order to build the stations gave archaeologists an unprecedented opportunity to study every layer of Rome’s past.
Rome’s Metro C line, which will augment the existing A and B lines, has been plagued by delays since it began nearly a decade ago, in part caused by the frequent discovery of archaeological remains.