 Complete the following phrase:  At some point following the fall of the Western Roman Empire, a retrenchment was built within the city, reducing it to its present size. This was done to make the citys perimeter more easily defensible, and similar reductions in city sizes were common around the Mediterranean region in the early Middle Ages. Although it was traditionally assumed that the retrenchment was built by the Arabs, it has been suggested that it was actually built by the Byzantine Empire in around the 8th century, when the 