Visitors to Rome will soon be able to discover a world of ancient treasures beneath their feet when the city opens dozens of previously unseen underground sites to the public.

They include the Ludus Magnus, the barracks beneath the Colosseum where gladiators assembled before entering the great arena to meet their fate; the well-preserved necropolis of Santa Rosa at the Vatican, with tombs from the 1st to the 5th centuries, and pagan temples.

Guided tours through the sites begin on Monday. Gianni Alemanno, the Mayor of Rome, said he hoped that the experiment would be repeated next year and that in future some of the sites would remain open throughout the summer. “There is a lot of unknown Rome to explore, not just the best-known sights,” he said.

The 30 underground marvels are rarely seen by tourists, or residents. “Hidden Rome is in front of everyone’s eyes but nobody notices it,” said Umberto Broccoli, the superintendent of cultural heritage in Rome. “A large part of Rome’s history lies underground.”

He singled out the auditorium of Maecenas, the wealthy close adviser to the Emperor Augustus, whose encouragement of poets and painters in 1st century Imperial Rome made his name a byword for patronage of the arts.

The ruins of his frescoed theatre for readings and performances, now below ground and protected by a modern roof, are tucked away in a small urban square that is all that remains of his once vast and magnificent horti, or gardens, on the Esquiline Hill.

Few visitors are aware that a 2,000-year-old underground aqueduct, the Acqua Virgo — originally built to supply the Baths of Agrippa near the Pantheon in 19BC and still used to bring water to the city — lies beneath the Renaissance-era Villa Medici, now the French Academy, and ends in the Baroque stone fantasy of the Trevi Fountain.

Tourists can also explore the frescoed 2nd century Temple of Mithras, the pagan cult, beneath the 17th Century Palazzo Barberini, which houses one of Rome’s foremost art collections.

Francesco Marcolini, the head of Zetema, the cultural foundation in charge of the project, said that next year 15 more underground sites would be added, including a Jewish necropolis in the grounds of Villa Torlonia, formerly the Rome residence of Benito Mussolini, the Fascist dictator.

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