Alexander the Great conquered the territory in the 4th century BC on his way to South Asia. In 330 BC, Alexander marched northward into Central Asia and founded the city of Alexandria near the Murgab River. Located on an important trade route, Alexandria later became the city of Merv. The ruins of Alexander's ancient city are still to be found and have been extensively researched. After Alexander's death his empire quickly fell apart. It was ruled by Seleucids before the satrap of Parthia declared independence. The Parthians – fierce, nomadic warriors from the north of Iran – then established the kingdom of Parthia, which covered present-day Turkmenistan and Iran. The Parthian kings ruled their domain from the city of Nisa – an area now located near the modern-day capital of Ashgabat – founded by Arsaces I (reigned c. 250–211 BC), and was reputedly the royal necropolis of the Parthian kings, although it has neither been established that the fortress at Nisa was a royal residence nor a mausoleum.