Parthia was a region of Persia. It was conquered by the Medes during the 7th century BC. Subsequently, it was incorporated into the Achaemenid Empire under Cyrus the Great in the 6th century BC. After the conquest of Persia by Alexander the Great, it became part of the Hellenistic Seleucid Kingdom. By the 3rd century BC, Parthia became independent. The Parthian Empire (247 BC – 224 AD) defeated the Romans under Crassus at Carrhae in 52 BC and a series of wars continued for the next two centuries.