In 64 A.D. a devastating fire blazed through Rome, destroying half the city. In the decades that followed, such familiar structures as Nero’s palace, the Colosseum and Trajan’s Baths rose from the ashes.

What did Rome look like before the fire? A fresco discovered this February, dating to the first century A.D., may hold the answer.

Italian archaeologist Elisabetta Carnaburgi discovered the fresco in a dark tunnel beneath the ruins of Trajan’s Baths, in central Rome. The large faded painting, 18 feet wide by 10 feet high, shows an unusual bird’s-eye view of an ancient city, with robust walls and seven defensive towers. The walls enclose residential buildings, small houses with loggia-adorned balconies, a palace and a theater. A river meanders through the heart of the city, much as the Tiber River flows through Rome.