Frescoed barracks which once housed the cavalry of the Emperor Hadrian's bodyguard have returned to light 19 centuries on, during excavations for a new underground train line in Rome.
In a find hailed as "unique" by archaeologists, weapons rooms, dormitories, kitchens and stables where some of ancient Rome's crack troops once lodged now lie open to the sky near the Colosseum, where the "Amba Aradam" stop of the Metro C line is being dug.
Uncovering broken pots, Roman coins or that archaeological staple, a series of low walls, is all in a day's work for head engineer Andrea Sciotti, particularly near the ancient forums and gladiator battling ground and training schools.
"But this time, the effect was different. The emotion crept up upon us," he told AFP over the noise of concrete-mixers and drills, marvelling at the excellent state of preservation of the vast site which covers 900 square metres (9,700 square feet).
Work here is steaming ahead to create the first "archaeological station" in Rome, which Francesco Prosperetti, the capital's superintendent of archaeology, hopes will outdo other impressive metro "museums" from Athens to Naples, Porto and Vienna.
"We will keep as much of the site as possible in the future station so that, when you're on your way to catch a train, you can look down on it all and enjoy the view," said Sciotti.
The digs for Rome's much-needed third metro line, which will connect 30 stations in the tourist-heavy Eternal City, began in 2007 but have been delayed repeatedly by the discovery of buried artefacts and it is not expected to be fully open before 2021.
- 'Unique discovery' -
"The challenge will be to create a space which will speak of Rome's underground to those on the move," Prosperetti said.
Amid the diggers and scaffolding lie the remains of 39 rooms of barracks where hundreds of soldiers -- the so-called "equites singulares augusti", one of the elite corps of the Praetorian Guard -- were housed during the 2nd century AD.
Archaeologists also found a collective grave on the site, where they have so far unearthed 13 adult skeletons and a bronze bracelet.
The cavalry guard, which escorted the Roman emperor whenever he left the city, were so fierce they were used by successive leaders to quash unruly mobs in street battles and boost military campaigns abroad.
Black and white mosaics decorate the barracks floors, and frescoes in Pompeian red can be seen on some of the remaining walls.
"When the call came they left their rooms, went along a corridor to the weapons room to collect their arms and headed off to where they were needed," said archaeologist Rossella Rea, describing the ruins as a "unique discovery".
The find brings the total number of known military garrisons in the area to five, with one of the most important resting under the nearby Saint John Lateran basilica, the pope's seat in Rome.
"In ancient times, this area was the Campus Martius, where, during the months of February and March, ceremonies and festivities were organised in honour of Mars, the god of war," Rea said.
While Romans celebrated with chariot races, dances and feasts in the street, the cavalry slept six to a room, ready to be called at any minute to seize their swords and shields, decorated with their emblem, the scorpion, and saddle up.