The siege of Amida was a military investment of the Roman fortified frontier city of Amida (modern Diyarbakır, Turkey) by the Sasanian Empire. It took place in AD 359 when the Sasanian army under king Shapur II invaded the eastern provinces of the Roman Empire. Shapur wanted to exploit the absence of the Roman Emperor Constantius II who was overseeing affairs in the western part of the Empire. The city fell, but the strategic gain was little. Ammianus Marcellinus, a Roman army officer, provided a vivid description of the siege in his work (Res Gestae). Ammianus served on the staff of Ursicinus, the Magister Equitum (master of horse) of the East, during the events of the siege. Background Persian When Shapur II took control of the Sasanian Empire, he sought to regain old territories previously lost to the Roman Empire. After crushing the Arabs in the south, he moved east to deal with nomadic forces, the most prominent being the Xionites. Following a prolonged struggle from (353-358) the Xionites were forced to conclude a peace, and their king, Grumbates, accompanied Shapur II in the war against the Romans. In 358 the Romans had failed to dissuade Shapur from attacking Mesopotamia, so the next year Shapur decided to invade. Shapur started the western campaign in 359. Roman Emperor Constantius II had increasingly been doubting the loyalty of General Ursicinus. As a result, he did not give him command of the Roman forces in the East, and instead gave it to Sabinianus. Ursicinus served as Magister Equitum (Master of Horse) while Sabinianus held the rank of Magister Peditum (Master of Foot) of the East. As events unfolded, Ursicinus became the 'de facto' commanding general of the Limitanei armies of Mesopotamia and Osrhoene, while Sabinianus continued as commander of Comitatus (the Field Army) of the East. As news of the Persian invasion spread, the civilian population of the region began to panic: Several Roman legions gathered at Amida. These included: Legio XXX Ulpia Victrix, Magnentius, Decentius, Superventores, Praeventores and a detachment of Legio X Fretensis. The garrison of Amida itself consisted of Legio V Parthica supported by an unidentified cavalry regiment. Ursicinus probably planned to use Amida as a base of operations against the Persian invasion. Preliminaries of the siege Shapur's plan was to bypass difficult fortress cities like Nisibis and march straight into Syria. The Sassanid Royal Army crossed the Tigris and