The Medici Fortress of Arezzo stands on the hill of San Donato, which dominates the city and the surrounding area. From there, the gaze ranges from the hills towards the Chianti to the west, to the slopes of the Pratomagno massif to the north-west, to the Catenaia and Poti Alps to the north-east and east, and to Mount Lignano to the south.On this hill and on the nearby hill of San Pietro, where the Duomo now stands, was the heart of the ancient city where the most important public monuments were concentrated.Although the many transformations that have occurred over the centuries have heavily transformed the appearance of this place, the archaeological remains we have left tell us its story.The hill was populated since the archaic Etruscan period (sixth century B.C.), when Arezzo was a powerful urban center, and in the fourth century B.C. it was included within the defensive walls.In the second century B.C. a massive building was raised, today visible outside the Fortress, between the bastions of the Spina and the Belvedere (fig. 1, n. 3). It is improperly defined "Capitolium" for its tripartite structure similar to the temples dedicated to the three main deities of the Roman Pantheon. Its religious destination is also deducted from the discovery of terracotta decorations and votive offerings.Heavy transformations were carried out in the area in Roman times, when the city of Arretium was the stage of an intense and rapid economic, demographic and urban development, linked to the expansion of the manufactures of a particular type of coral red ceramic with a resistant and shiny surface: the Terra Sigillata Aretina.Sumptuous houses decorated with paintings on the walls and mosaic floors were built along the main streets of the city and public buildings were built for entertainment and recreation, such as the Amphitheater in the lower part of the city, the Baths and the Theater (fig. 1, n. 4).Of this important entertainment building remains today only part of the terraces for spectators, visible along Viale Buozzi between the bastions “del Belvedere” and “della Chiesa”. Not far away, structures and a cistern attributable to thermal baths were found, probably fed by the public aqueduct which, coming from the north, crossed the top of the hill to bring water to the city. Another monumental cistern was in the area between the current entrance of the Fortress and the Prato.On the northern side of the hill, now inside the Fortress, a building dating back to the first century A.D. was recently found (fig. 1, n. 7). It has beautiful mosaic floors and painted walls (fig. 2). It is believed that the central room was used a century later as a place of worship for the God Mithras, whose originally oriental cult was particularly spread in places characterized by a lively multicultural society. This must have accured in Arretium at that time, thanks to the arrival of labor for ceramic workshops from other areas of the Empire.