After the partition of the Empire in 395, the Peloponnese became a part of the East Roman or Byzantine Empire. The devastation of Alaric's raid in 396–397 led to the construction of the Hexamilion wall across the Isthmus of Corinth. Through most of late antiquity, the peninsula retained its urbanized character: in the 6th century, Hierocles counted 26 cities in his "Synecdemus". By the latter part of that century, however, building activity seems to have stopped virtually everywhere except Constantinople, Thessalonica, Corinth, and Athens. This has traditionally been attributed to calamities such as plague, earthquakes and Slavic invasions. However, more recent analysis suggests that urban decline was closely linked with the collapse of long-distance and regional commercial networks that underpinned and supported late antique urbanism in Greece, as well as with the generalized withdrawal of imperial troops and administration from the Balkans.