Turning next to foreign policy, Julian saw the previously unchecked military incursions of Shapur II of Persia against the Eastern Roman provinces as posing the greatest external threat. After many failed earlier attempts, the Persian king launched a more successful second campaign against the Romans and captured Amida in 359, controlling the headwaters of the Tigris and the entrance to Asia Minor from the east. A Roman offensive was desperately needed to halt Shapur.