Question: In which battle the Roman Emperor from 361 to 363 was killed?

Context paragraphs:
Battle of Maranga: The Battle of Maranga occurred in 363 AD, shortly after the Battle of Ctesiphon.  The Romans repelled a Sasanian attack while sustaining minimal losses.  However, the army's lack of supplies continued to threaten the army, and soon afterwards the emperor Julian was killed at the Battle of Samarra.

Julian's Persian War: Julian's Persian War, or the Perso-Roman War of 363, was the last undertaking of the Roman emperor Julian, begun in March 363.  It was an aggressive war against the Persian Empire ruled by the Sassanian king Shapur II.  Shapur is believed to have expected an invasion by way of the Tigris valley.  Julian sent a detachment to join with his ally Arshak II of Armenia and take the Tigris route.  Meanwhile, with his main army he advanced rapidly down the Euphrates valley, meeting only scattered opposition, and reached the walls of the Persian capital Ctesiphon where he met and defeated the Persian army at the Battle of Ctesiphon (363).  Unable to take the city, and with a faltering plan of campaign, He was misled by Persian spies into burning his fleet and taking a disadvantageous route of retreat in which his army was constantly harassed and his progress crawled to a halt.

Fadilla: Annia Aurelia Fadilla, most commonly known as Fadilla (159-died after 211) was an influential Roman Princess and was one of the daughters born to Roman Emperor Marcus Aurelius and Roman Empress Faustina the Younger.  She was a sister to Roman Empress Lucilla and Roman Emperor Commodus.  Fadilla was named in honor of her late maternal aunt Aurelia Fadilla.  The cognomen Fadilla, was the cognomen of the mother and a half-sister of the previous Roman Emperor Antoninus Pius.  Her maternal grandparents were Roman Emperor Antoninus Pius and Roman Empress Faustina the Elder and her paternal grandparents were Domitia Lucilla and praetor Marcus Annius Verus.

Oribasius: Oribasius or Oreibasius (Greek: Ὀρειβάσιος ; c. 320 – 403) was a Greek medical writer and the personal physician of the Roman emperor Julian the Apostate.  He studied at Alexandria under physician Zeno of Cyprus before joining Julian's retinue.  He was involved in Julian's coronation in 361, and remained with the emperor until Julian's death in 363.  In the wake of this event, Oribasius was banished to foreign courts for a time, but was later recalled by the emperor Valens.

Against the Galilaeans: Against the Galilaeans (Ancient Greek: Κατὰ Γαλιλαίων ; Latin: "Contra Galilaeos" ), meaning Christians, was a Greek polemical essay written by the Roman Emperor Flavius Claudius Julianus, commonly known as Julian the Apostate, during his short reign (361–363).  Despite having been originally written in Greek, it is better known under its Latin name, probably due to its extensive reference in the polemical response "Contra Julianum" by Cyril of Alexandria.

Eutropius (historian): Flavius Eutropius was an Ancient Roman historian who flourished in the latter half of the 4th century AD.  He held the office of secretary ("magister memoriae") at Constantinople, accompanied the Emperor Julian (361–363) on his expedition against the Persians (363), and was alive during the reign of Valens (364–378), to whom he dedicates his "Breviarium historiae Romanae" and where his history ends.  Possibly he held higher state offices in later years, becoming Praetorian prefect for Illyria in 380 and - together with emperor Valentinian II - consul in 387.  However, it is a question of academic discussion whether the Eutropius holding these offices is really to be identified with the historian.

Constantius II: Constantius II (Latin: "Flavius Julius Constantius Augustus" ; 7 August 317 – 3 November 361) was Roman Emperor from 337 to 361.  The second son of Constantine I and Fausta, he ascended to the throne with his brothers Constantine II and Constans upon their father's death.

Julian (emperor): Julian (Latin: "Flavius Claudius Iulianus Augustus" ; Greek: Φλάβιος Κλαύδιος Ἰουλιανὸς Αὔγουστος ; 331/332  – 26 June 363), also known as Julian the Apostate, was Roman Emperor from 361 to 363, as well as a notable philosopher and author in Greek.

Dagalaifus (Roman Consul, 366): Dagalaifus was a pagan of Germanic descent.  In the year 361, he was appointed by Emperor Julian as comes domesticorum (Commander of the Household Guard).  He accompanied Julian on his march through Illyricum to quell what remained of the government of Constantius II that year.  He led a party into Sirmium that arrested the commander of the resisting army, Lucillianus.  In the spring of 363, Dagalaifus was part of Julian’s ultimately-disastrous invasion of Persia.  On June 26, while still campaigning, Julian was killed in a skirmish.  Dagalaifus, who had been with the rear guard, played an important role in the election of the next emperor.  The council of military officers (including Dagalaifus) finally agreed on the new "comes domesticorum", Jovian, to succeed Julian.  Jovian was a Christian whose father Varronianus had himself once served as "comes domesticorm".

Battle of Ctesiphon (363): The Battle of Ctesiphon took place on May 29, 363 between the armies of Roman Emperor Julian and an army of the Sasanian Empire (during Shapur II's reign) outside the walls of the Persian capital Ctesiphon.  The battle was a Roman victory, although Julian was killed following the subsequent Battle of Samarra and the Roman forces found themselves unable to continue their campaign as they were too far from their supply lines.

Supporting paragraphs: Battle of Maranga Julian (emperor)
Answer: Battle of Samarra