The Pantheon "temple of all the gods" is a former Roman temple and since the year 609 a Catholic church (Basilica di Santa Maria ad Martyres or Basilica of St. Mary and the Martyrs), in Rome, on the site of an earlier temple commissioned by Marcus Agrippa during the reign of Augustus (27 BC – 14 AD). It was rebuilt by the emperor Hadrian and probably dedicated c. 126 AD.

The Aurelian Walls are a line of city walls built between 271 AD and 275 AD in Rome, Italy, during the reign of the Roman Emperors Aurelian and Probus. They superseded the earlier Servian Wall built during the 4th century BC. The walls enclosed all the seven hills of Rome plus the Campus Martius and, on the right bank of the Tiber, the Trastevere district. The river banks within the city limits appear to have been left unfortified, although they were fortified along the Campus Martius. The size of the entire enclosed area is 1,400 hectares (3,500 acres)The wall cut through populated areas: in reality the city at the time embraced 2,400 hectares or 6,000 acres.[citation needed] Pliny the Elder in the first century A.D. suggested that the densely populated areas, 'extrema tectorum' (the limits of the roofed areas) extended 2.8 kilometres (1.7 mi) from the Golden Milestone in the Forum .