War with the Seleucid Empire thumb|300px|Map of Bactria during the Hellenistic Age Little is known of his reign until 208 BC when he was attacked by Antiochus III the Great, whom he tried in vain to resist on the shores of the river Arius (Battle of the Arius), the modern Harirud. Although he commanded 10,000 horsemen, Euthydemus initially lost a battle on the Arius and had to retreat. He then successfully resisted a three-year siege in the fortified city of Bactra, before Antiochus finally decided to recognize the new ruler, and to offer one of his daughters to Euthydemus's son Demetrius around 206 BC. As part of the peace treaty, Antiochus was given Indian war elephants by Euthydemus.
War with the Seleucid Empire thumb|300px|Map of Bactria during the Hellenistic Age Little is known of his reign until 208 BC when he was attacked by Antiochus III the Great whom he tried in vain to resist on the shores of the river Arius (Battle of the Arius), the modern Harirud Although he commanded 10,000 horsemen, Euthydemus initially lost a battle on the Arius and had to retreat. He then successfully resisted a three-year siege in the fortified city of Bactra, before Antiochus finally decided to recognize the new ruler, and to offer one of his daughters to Euthydemus's son Demetrius around 206 BC. As part of the peace treaty Antiochus was given Indian war elephants by Euthydemus.