Constantius repeatedly defended the eastern border against invasions by the aggressive Sassanid Empire under Shapur. These conflicts were mainly limited to Sassanid sieges of the major fortresses of Roman Mesopotamia, including Nisibis (Nusaybin), Singara, and Amida (Diyarbakir). Although Shapur seems to have been victorious in most of these confrontations, the Sassanids were able to achieve little. However, the Romans won a decisive victory at the Battle of Narasara, killing Shapur's brother, Narses. Ultimately, Constantius was able to push back the invasion, and Shapur failed to make any significant gains.