sentences:  Later that year he took the Parthian capital, Susa, and deposed the Parthian King Osroes I.However, the Romans did not Romanize the entire Parthian Empire, leaving Parthamaspates as a puppet king on the throne to rule over former Parthian lands with the exclusion of modern Iraq, which became Assyria and Mesopotamia.At its greatest extent, the southern borders were the deserts of Arabia and the Sahara, that represented a natural barrier to prevent expansion.