In the winter of 48/47 BC, Julius Caesar was under siege in Alexandria by the armies of Achillas, guardian and general for King Ptolemy XIII Theos Philopator. Mithridates raised an army and came to Caesar's relief. In the aftermath of the Battle of Zela, Caesar made him king of the Bosporan Kingdom. Mithridates's niece Dynamis and her husband Asander were the ruling monarchs at the time, and were defeated by Mithridates's army.