By the late 3rd century, Roman fortunes on the eastern frontier improved dramatically. During a period of civil upheaval in Persia, emperor Carus led a successful campaign into Persia essentially uncontested, sacking Ctesiphon in 283 AD. During the reign of the Tetrarchy, emperors Diocletian and Galerius brought a decisive conclusion to the war, sacking Ctesiphon in 299 AD and expanding the Roman eastern frontier dramatically with the Treaty of Nisibis. The treaty brought lasting peace between Rome and the Sassanids for almost four decades until the end of Constantine the Great's reign. In 337 AD, Shapur II broke the peace and began a 26-year conflict, attempting with little success to conquer Roman fortresses in the region. After early Sassanid successes including the Battle of Amida in 359 AD and the Siege of Pirisabora in 363 AD, Emperor Julian met Shapur in 363 AD in the Battle of Ctesiphon outside the walls of the Persian capital. The Romans were victorious but were unable to take the city, and were forced to retreat due to their vulnerable position in the middle of hostile territory. Julian was killed in the Battle of Samarra during the retreat, possibly by one of his own men.