Nisa (also Parthaunisa) was an ancient city, 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 be founded by Arsaces I (reigned c. 250 BC–211 BC), and was reputedly the royal necropolis of the Parthian kings, although it has not been established that the fortress at Nisa was either a royal residence or a mausoleum.

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. Nisa was later renamed Mithradatkirt ("fortress of Mithradates") by Mithridates I of Parthia (reigned c. 171 BC–138 BC). Nisa was totally destroyed by an earthquake, which occurred during the first decade BC. The fortress at Nisa was declared a World Heritage Site by UNESCO in 2007.