A steppe people from east of the Caspian Sea who entered northeastern Iran and set up a kingdom at the expense of the Seleucid empire and Bactria. The Parthian empire existed from 247 BC-224 AD. The earliest Parthian capital was probably at Dara; two of the later capitals were Nisa and Hecatompylos. Between 160-140 BC, Mithridates I extended the Parthian state into an empire, incorporating Iran and most of Mesopotamia, which survived 350 years of almost constant conflict with the Seleucids and later the Romans until its overthrow by the Sassanians in the early 3rd century AD. When flourishing, the Parthians established an oriental empire with Greek civilization grafted on. Their culture and location was an important intermediary between the Near and Far East and they controlled most of the trade routes between Asia and the Greco-Roman world. The silk road to China was opened under Mithradates II (124/123-87 BC). The Parthians were also famous for their superlative horsemanship.