The Battle of the Arius was fought in 208 BC between the Seleucids and the Bactrians. The Seleucids were led by Antiochus III the Great, who launched an invasion of Bactria. He was victorious, and went on to besiege the capital of Bactra (modern-day Balkh.) After a siege lasting three years, a peace was agreed in which Euthydemus was recognized as an ally, obtaining one of Antiochus's daughters as a wife.