More than a century would pass before Rome again lost military ascendancy over its external enemies. However, dozens of formerly thriving cities, especially in the Western Empire, had been ruined. Their populations dead or dispersed, these cities could not be rebuilt, due to the economic breakdown caused by constant warfare. The economy was also crippled by the breakdown in trading networks and the debasement of the currency. Major cities and towns, including Rome itself, had not needed fortifications for many centuries, but now surrounded themselves with thick walls.