Margiana (Greek: Μαργιανή Margianḗ, Old Persian: Marguš, Middle Persian: Marv) is a historical region centred on the oasis of Merv and was a minor satrapy within the Achaemenid satrapy of Bactria, and a province within its successors, the Seleucid, Parthian and Sasanian empires.

It was located in the valley of the Murghab River 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. Margiana bordered Parthia to the south-west, Aria in the south, Bactria in the east and Sogdia in the north.

Historians currently disagree as to the exact history of Margiana prior to the Achaemenid conquest. It is considered part of a Bronze Age civilisation, the Bactria–Margiana Archaeological Complex (short BMAC), also known as the Oxus civilisation. Some historians have argued that a kingdom was established and an urban society had begun to develop surrounding the oasis. It has also been postulated the region existed as part of a major Iranian state centred in Chorasmia that controlled Aria, Sogdia, Parthia and Margiana. Other historians have noted that whilst advanced irrigation had begun in the 7th century BC, the existence of such a state is unlikely. It has been also suggested that Margiana was part of the satrapy of Bactria under the Median Empire.

Margiana was conquered by the Persian king Cyrus the Great between 545 and 539 BC and remained as part of the satrapy of Bactria. Cyrus also founded the city of Merv. After Darius the Great's victory over the Magian usurper, Gaumata, in September 522 BC, revolts spread throughout the empire. The revolt in Margiana, led by a certain Frâda (Phraates), was suppressed almost immediately, in December 521 BC by Dadarsi, the Satrap of Bactria. In the Aramaic version of the Behistun Inscription, it is claimed that 55,423 Margians were killed and 6,972 taken captive in the aftermath of the revolt. Margiana was separated from the satrapy of Bactria and joined to the satrapy of Aria at some point after the rule of Darius the Great.

Following the Battle of Gaugamela in 331 BC, in which Alexander the Great defeated Darius III, Darius III began his retreat to Bactria, but was overthrown by the Satrap of Bactria, Bessus, who continued the retreat eastward through Aria and Margiana. Bessus, who had expected an attack from Alexander along the Silk Road, was surprised when Alexander had advanced through Gedrosia and Arachosia and crossed the Hindu Kush mountains in 329 BC to invade Bactria. Bessus fled north to Sogdia where he too was betrayed and was handed over to Alexander by his courtiers, Spitamenes and Datames.

In July 329 BC, as Alexander founded the city of Alexandria Eschate on the northern border of Sogdia, Spitamenes led a revolt and besieged the Sogdian capital of Maracanda. A Scythian incursion into Sogdia prevented Alexander from responding personally, however, once he had defeated the Scythians in the Battle of Jaxartes, he marched south to relieve Maracanda causing Spitamenes to move south and attack Balkh in the winter of 329 BC. In the spring of 328 BC, Alexander sent his general Craterus to fortify Margiana, where he established a garrison in Merv and re-founded the city as Alexandria in Margiana. Alexander's general Coenus defeated Spitamenes in the Battle of Gabai in December 328 BC, and subsequently in the following year Sogdia was merged with Bactria to form a single satrapy under the rule of Philip.

Upon Alexander's death in 323 BC, the empire was partitioned between his generals at the Partition of Babylon and according to some historians, Philip remained as satrap of Bactria, however, it has also been suggested that he was in fact only satrap of Sogdia. Disagreements between the generals led to another meeting and in the Partition of Triparadisus in 321 BC, Philip was replaced as satrap of Bactria and Sogdia by Stasanor. During the Wars of the Diadochi, Stasanor remained neutral, however after the Babylonian War of 311–309 BC, Margiana came under the control of Seleucus I Nicator. In c. 280 BC, Margiana was devastated by the nomadic Parni tribes and several cities were destroyed. Seleucus responded by sending his general Demodamas to repel the nomads. Under Seleucus' successor, Antiochus I Soter, the oasis of Alexandria in Margiana was surrounded by a wall over 300 km long and the city was re-built and re-founded as Antiochia in Margiana as the capital of a separate satrapy of Margiana in an effort to secure communications and trade routes from Antiochus' capital in Mesopotamia to the far east. Margiana was successfully defended by Diodotus, the satrap of Bactria, against an invasion by the Parni in c. 239/238 BC. The invasion demonstrated that Seleucus II Callinicus was unable to respond to threats in the East and therefore Diodotus, who had begun pushing for his independence in c. 245 BC, abandoned hopes of remaining part of the Seleucid Empire and declared himself king, thus establishing what is now known as the Greco-Bactrian Kingdom.

Margiana was conquered by the Parthians under Mithridates I of Parthia in c. 170 BC. The defeat of the Yuezhi people in 175 BC caused many Yuezhi to flee westwards, displacing the Saka as a result, leading to a mass movement of Saka and Yuezhi towards Sogdia and Bactria. Around 140 BC the Saka invaded Parthian territory through Margiana, venturing as far as Media in central Iran and continuing to harass the Parthians until 124 BC, in the course of which they defeated and killed two successive Parthian kings. The Yuezhi, who had settled in Sogdia along the Oxus, controlled Margiana until 115 BC when Mithridates II of Parthia re-established control over the east, forcing the Yuezhi to move south into Bactria. In 53 BC, 10,000 Roman prisoners captured by the Parthians after the Battle of Carrhae in Upper Mesopotamia were settled in Antiochia in Margiana. The Yuezhi went on to conquer the remaining Greek territories in Paropamisadae and establish the Kushan Empire.