The Siege of Bactra lasted from 208 to 206 BC. It was a siege on the city of Bactra by Seleucid Empire after defeating the Greco-Bactrians at the Battle of the Arius the Seleucids besieged the capital of Bactria until news from the west of his dominions and lack of progress against the city led Antiochus to negotiate peace with Euthydemus and lift the siege. In the peace that was agreed Antiochus recognized Euthydemus as an ally, and he gave one of his daughters as a wife to the Demetrius, Euthydemus's eldest son.
The Greco-Bactrians had recently been defeated at the Battle of the Arius by Antiochus III. After this defeat, Euthydemus retreated to Zariaspa, likely a distract of Bactra. The Greco-Bactrians were able to hold out long enough against Antiochus for his fortunes in the west to deteriorate.
After 2 years of laying siege to Bactra, Antiochus's fortunes to the west of his empire were deteriorating. Euthydemus then sent his son, Demetrius, as his representative. Impressed at Demtrius's well representation worthy of that of a royal, Antiochus offered him one of his daughter's and agreed to a peace treaty.