Volubilis. The effective control of Roman legionaries, however, was up to the area of Sala Colonia (the castra "Exploratio Ad Mercurios", south of Sala Colonia, is the southernmost Roman settlement discovered until now). Some historians, like Leo Africanus, believe the Roman frontier reached the area of Casablanca, founded by the Romans as a port named "Anfa". Indeed, the modern city of Azemmour in central Morocco lies on the ancient Azama, a trading port of Phoenician and later Roman origins. Still today can be seen the remains of a Roman deposit for grain in the so-called "Portuguese cisterns". Pliny the Elder described in some detail the area south of the Atlas Mountains, when Gaius Suetonius Paulinus undertook a military expedition in 41: Roman province During the reign of the Numidian King Juba II, Emperor Augustus had already founded three colonias (with Roman citizens) in Mauretania close to the Atlantic coast: Iulia Constantia Zilil, Iulia Valentia Banasa and Iulia Campestris Babba. This western part of Mauretania was to become the province called Mauretania Tingitana shortly afterwards. The region remained a part of the Roman Empire until 429, when the Vandals overran the area and Roman administrative presence came to an end. The most important city of Mauretania Tingitana was Volubilis. This city was the administrative and economic center of the province in western Roman Africa. The fertile lands of the province produced many commodities such as grain and olive oil, which were exported to Rome, contributing to the province's wealth and prosperity. Archaeology has documented the presence of a Jewish community in the Roman period. The principal exports from Mauretania Tingitana were purple dyes and valuable timber. Tingitana also supplied Rome with agricultural goods and animals, such as lions and leopards. The native Mauri were highly regarded and recruited by the Romans as soldiers, especially as light cavalry. Clementius Valerius Marcellinus is recorded as the governor (praeses) between 24 October 277 and 13 April 280. According to tradition, the martyrdom of St Marcellus took place on 28 July 298 at Tingis (Tangier). During the Tetrarchy (Emperor Diocletian's reform of Roman governmental structures in 297), Mauretania Tingitana became part of the Diocese of Hispaniae, 'the Spains', and, by extension, part of the Praetorian prefecture of Gaul, thus it was across the sea from the European territory of Diocese and Prefecture it belonged to. Mauretania Caesariensis was in the Diocese of Africa. Lucilius Constantius