[[Berkas:Antoninianus-Tranquillina-Gordian III-s2539.jpg|thumb|left|300px|Koin yang dikeluarkan untuk merayakan pernikahan Gordian dan Sabina Tranquillina, ''[[Augusta (gelar)|Augusta]]''.]]
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In the 3rd century, the Roman frontiers weakened against the Germanic tribes across the [[Rhine]] and [[Danube]], and the [[Sassanid Empire|Sassanid]] kingdom across the [[Euphrates]] increased its own attacks. When the Persians under [[Shapur I]] invaded [[Mesopotamia]], the young emperor opened the doors of the [[Temple of Janus (Roman Forum)|Temple of Janus]] for the last time in Roman history, and sent a huge army to the East. The Sassanids were driven back over the Euphrates and defeated in the [[Battle of Resaena]] (243). The campaign was a success and Gordian, who had joined the army, was planning an invasion of the enemy's territory, when his father-in-law died in unclear circumstances. Without Timesitheus, the campaign, and the emperor's security, were at risk.
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Marcus Julius Philippus, also known as [[Philip the Arab]], stepped in at this moment as the new Praetorian Prefect and the campaign proceeded. In the beginning of 244, the Persians counter-attacked. Persian sources claim that a battle was fought ([[Battle of Misiche]]) near modern [[Fallujah]] ([[Iraq]]) and resulted in a major Roman defeat and the death of Gordian III<ref>''Res Gestae Divi Saporis'', 3-4 (translation of Shapurs' inscription at Naqsh-i Rustam)</ref>. Roman sources do not mention this battle and suggest that Gordian died far away, upstream of the Euphrates. Although ancient sources often described Philip, who succeeded Gordian as emperor, as having murdered Gordian at Zaitha (Qalat es Salihiyah), the cause of Gordian's death is unknown.