Remains of a large auditorium built in 123 AD by Emperor Hadrian have been uncovered under Piazza Venezia in Rome during excavations for the new underground metro line's station, according to this Guardian article. The building has a marble floor and is believed to have been used as an art center. Archeologists spent five years excavating the site which is now open to the public. Piazza Venezia is a main transportation hub in central Rome and site of the Victor Emmanuel II monument, Italy's first king. Nearby are the Capitoline Museums.
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Victor Emmanuel II Monument in Piazza Venezia © by James Martin, Europe Travel