Parthia, an ancient region of Persia, encompassing what is now northeastern Iran. In 248 B.C. Arsaces, a Scythian nomad chieftain, founded the Parthian kingdom. By 129 B.C. the Parthians had conquered Persia and Mesopotamia from the Seleucid Kingdom, establishing an empire. In theory the Parthian Empire was a reconstruction of the ancient Persian Empire, but its emperors never established strong central rule over vassal nobles and kings. The Parthian emperors fought many wars with the Roman Empire, their neighbor to the west. In 226 A.D. Ardashir I of Persis (south Persia) overthrew the Parthian dynasty and founded the Sassanid Empire.