Margu (Latin: Margiana from Greek: Μαργιανή) was a satrapy of the Achaemenid Empire. The ruler who lost a Bactrian revolt is mentioned as a Margian in the Behistun inscriptions of ca. 515 BCE by Darius Hystaspis. It is not mentioned as a satrapy in the inscription, because it was included in a larger satrapy of the empire. It was located in the valley of the river Murghab which has its sources in the mountains of Afghanistan, and passes through Murghab District in modern Afghanistan, and then reaches the oasis of Merv in modern Turkmenistan. Merv was the center of Margiana.