Coinciding with the decline of the Roman Empire, many "barbarian" tribes passed through the Balkans, most of whom did not leave any lasting state. During these "Dark Ages", Eastern Europe, like Western Europe, regressed culturally and economically, although enclaves of prosperity and culture persisted along the coastal towns of the Adriatic and the major Greek cities in the south.[18] As the Byzantine Empire withdrew its borders more and more, in an attempt to consolidate its waning power, vast areas were de-urbanised, roads abandoned and native populations may have withdrawn to isolated areas such as mountains and forests.[18]