Nisa (Ancient Greek: Νῖσος and Νίσα and Νίσαιον) (also Parthaunisa) was an ancient settlement of the Iranian peoples, located near (modern-day) Bagir village, 18 km southwest of Ashgabat, Turkmenistan. Nisa is described by some as the first seat of central government of the Parthians. It is traditionally assumed to have been founded by Arsaces I (reigned c. 250 BC–211 BC) and was reputedly the royal residence of the Parthian kings, although it has not been established that the fortress at Nisa was either a royal residence or a mausoleum.
Nisa was a major trading hub in the Parthian Empire. Nisa was later renamed Mithradatkirt Parthian: 𐭌𐭕𐭓𐭃𐭕𐭊𐭓𐭕 ("fortress of Mithradates") by Mithridates I of Parthia (reigned c. 171 BC–138 BC). The region was famous for the fast and beautiful horses.
Nisa was totally destroyed by an earthquake, which occurred during the 1st decade BC.
Excavations at Nisa have revealed substantial buildings, mausoleums and shrines, many inscribed documents and a looted treasury. Many Hellenistic art works have been uncovered, as well as a large number of ivory rhytons, the outer rims (coins) decorated with Iranian subjects or classical mythological scenes.