The Battle of the Arius was an engagement that was fought in 208 BC between the Seleucid Empire and the Greco-Bactrian Kingdom. The Seleucids were led by Antiochus III the Great, who launched an invasion of Bactria to recover his ancestor's past dominions. He would go on to be victorious in this battle, and would later go on to besiege the Bactrians at their capital of Bactra for three years.

The Seleucid Empire was a Greek power in West Asia during the Hellenistic period. It was founded in 312 BC by the Macedonian general Seleucus I Nicator, following the division of the Macedonian Empire founded by Alexander the Great, and ruled by the Seleucid dynasty until its annexation by the Roman Republic under Pompey in 63 BC.