Julian's Persian expedition

Julian's Persian expedition began in March 363 AD and was the final military campaign of the Roman emperor Julian. The Romans fought against the Sasanian Empire, ruled at the time by Shapur II.

Aiming to capture the Sasanians' winter capital of Ctesiphon, Julian assembled a large army. In order to mislead the opponent and to carry out a pincer attack, he sent a detachment to join with his ally Arshak II of Arsacid Armenia to take the Tigris route from the north. Meanwhile, his main army and a large fleet, facing little opposition, advanced rapidly down the Euphrates, destroying several well-fortified cities along the way. The ships then reached the walls of Ctesiphon, where a large Sasanian force had assembled in its defense.

The Romans won a victory outside the city, but the northern army failed to arrive, and the fortified capital seemed impregnable. Due to these complications, Julian did not attempt to besiege the city, instead burning the Roman fleet of supplies and leading a march into Persia's interior. Shapur II's army, however, took lengths to avoid a full-scale battle and used a scorched earth strategy; as a result, Julian's army soon faced supply problems and had to retreat to the north. Shapur II's army pursued the retreating Romans, ceaselessly harassing the retreat through skirmishes. Julian died of wounds from one of these skirmishes and his successor, Jovian, agreed to surrender under unfavorable terms in order to save the remnants of his demoralized and exhausted army from annihilation.

The Treaty of 363 transferred multiple regions and frontier fortresses, including Nisibis and Singara. In addition to territorial concessions, Rome renounced its alliance with Armenia, giving Shapur II the opportunity to invade and annex it.