Large-scale excavations in the city center have unraveled the stages of Beirut's growth since the Bronze and Iron ages. The ancient Tell of Beirut, north of Martyrs' Square, constituted the fortified center of the city during the Canaanite, Phoenician, Persian and Hellenistic periods. Starting the sixth century B.C., urban growth took place outside the fortified center (Acropolis) and extended as far west and south as today's hotel district and Emir Bechir street. Under Augustus, Beirut acquired the status of a Roman colony (Colonia Julia Augusta Felix Berytus) and its center moved from the ancient Tell to the present Nejmeh Square area. Delimited by prewar archeological work, the Roman Forum site with related public buildings was confirmed by recent excavations. Byzantine Beirut followed the Roman urban topography as indicated by remains of residential and commercial quarters. The celebrated Law School, founded in the early third century A.D., has still not been unequivocally located in the Nejmeh area. From Crusader and Mamluk Beirut, a ditch of the medieval fortification walls was found parallel to Patriach Hoyek street, as well as the watch towers, the Bourj, southeast of Martyrs' Square. The ancient Tell revealed part of the Crusader castle. From the Ottoman period, excavations revealed a series of harbor walls to the north of the Souks, between Khan Antoun Bey and the Majidiya mosque.