Diodotus II reversed his father's policy: This battle between Seleucus II and Arsaces took place around 228 BC. It is unclear whether Diodotus was actively involved in the battle or simply agreed to remain neutral, thereby leaving Arsaces free to bring all his forces to bear on the invading Seleucid army. Sometime after this, around 225 BC, Diodotus was killed by Euthydemus I, who usurped the throne and founded the Euthydemid dynasty. W. W. Tarn proposed that Diodotus I had married a Seleucid princess as a second wife and had a daughter who was married to Euthydemus, making him Diodotus II's brother-in-law. There is, however, no evidence for the existence of either of these women and the theory no longer enjoys credence with contemporary scholars. Archaeological evidence reveals that the city of Ai-Khanoum was besieged around 225 BC, an event which Holt connects with Euthydemus' seizure of power. It seems therefore that there was a period of civil war, culminating in Euthydemus' victory—a reconstruction that seems to be confirmed by numismatic evidence. Most scholars have treated the alliance with Arsaces as a response to the threat from Seleucus II. Tarn suggested that Euthydemus I's usurpation was a reaction to the alliance. Frank Holt proposes the opposite: that the alliance with Arsaces was a response to the outbreak of civil war with Euthydemus. Coinage Diodotus II largely continued the minting patterns laid down by his father. There were two mints, which issued gold, silver and bronze coinage. The precious metal coinage consisted of gold staters and silver tetradrachms, drachms, and hemidrachms on the Attic weight standard. These coins have the head of a male figure on the obverse shown wearing the diadem—a band of cloth wrapped around the head, with two strips hanging down the back, which had been the standard symbol of Hellenistic kingship since the time of Alexander the Great. The reverse of these coins depicted Zeus preparing to throw his thunderbolt. As mentioned above, during Diodotus I's reign, two different figures appeared on the obverses—an older figure ('series A') and a younger figure ('series C & E'), who are identified with Diodotus I and Diodotus II respectively. Series A and C probably minted at Ai-Khanoum or at Bactra, while Series E was minted at a second mint, which Frank Holt tentatively identifies with Bactra. This mint produced coinage in a smaller quantity and at a lower quality than