mention this battle only as an insignificant setback and suggest that Gordian died elsewhere. Certainly, the Sassanids had not been cowed by the previous battles with Rome and in 253 AD the Sassanids under Shapur I penetrated deeply into Roman territory several times, defeating a Roman force at the Battle of Barbalissos and conquering and plundering Antiochia in 252 AD following the Siege of Antiochia. The Romans recovered Antioch by 253 AD, and Emperor Valerian gathered an army and marched eastward to the Sassanid borders. In 260 AD at the Battle of Edessa the Sassanids defeated the Roman army and captured the Roman Emperor Valerian. 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. There were several future wars, although all brief and small-scale, since both the Romans and the Sassanids were forced to deal with threats from other directions during the 5th century. A war against Bahram V in 420 AD over the persecution of the Christians in Persia led to a brief war that was soon concluded by treaty and in 441 AD a war with Yazdegerd II was again swiftly concluded by treaty after both parties battled threats elsewhere. Collapse of the Western Empire (402–476 AD) Many theories have been advanced in way of explanation for