Although Armenia had been conquered and devastated by the Sassanid king Shapur II in 367/368, Pap was restored to the throne at a young age with Roman assistance in 370.
Early in his reign, Armenia and Rome won a joint victory over the Persians at the Battle of Bagavan, and some former territories of the kingdom were reconquered by the efforts of his sparapet (general-in-chief) Mushegh Mamikonian.
[1][2][a] Armenian historian Hakob Manandian considered it possible that Pap was actually the son of Parandzem by her first husband Gnel (Arshak's nephew).
[2] Historian Albert Stepanyan argues that Pap was in fact Arshak's son, but that he was initially legally regarded as Gnel's son, as Arshak had married Paradzem in an Iranian-style levirate marriage called stūr ī būtak or čakarīh, whereby a childless widow would marry one of her late husband's agnatic relatives to provide her deceased husband with an heir.
[4] Historian Nina Garsoïan, on the other hand, contends that Pap must have been Arshak's legitimate son and heir, as even the sources extremely hostile to him never question his legitimacy.
[12][b] Queen Parandzem and Prince Pap took refuge with the royal treasure in the fortress of Artogerassa (Artagers), defended by a troop of azats (lesser Armenian nobles).
[13] Faustus also mentions two Armenian nakharars (magnates), Meruzhan Artsruni and Vahan Mamikonian (possibly identifiable with Ammianus's Artabanes), in leadership positions under Shapur II's suzerainty, as well as Zik and Karen who carried Persian noble titles.
[16] Valens sent him to stay at Neocaesarea in Pontus Polemoniacus, 300 kilometres (190 mi) from the Armenian border, where Pap received "liberal support and education.
"[16][17] In 369, at the request of sparapet Mushegh Mamikonian (according to Faustus) or of Cylaces and Artabanes (according to Ammianus), Valens allowed Pap to return to Armenian territory.
[17] Valens was reluctant to bestow a royal title upon Pap as this would violate an earlier treaty signed by Jovian in July 363, whereby Rome had pledged not to intervene in Armenian affairs.
Shapur II also began systematically persecuting the local Christians, destroying churches, erecting fire temples and forcing conversion to Zoroastrianism.
[23][g] Faustus of Byzantium gives considerable credit for the victory to Mushegh Mamikonian and writes that Pap observed the battle from the nearby height of Mount Npat.
[23] Shapur II was unable to confront the massive Roman buildup in Armenia as a result of his preoccupation with Kushan attacks in the eastern part of his empire.
[36][37] Still others regard Pap's conflict with the clergy as the result of his steps to restrain the excessive power of the church, which had accumulated significant estates and wealth in the form of the charitable institutions created by Nerses during Arshak II's reign.
[1][38] The conflict between the king and the patriarch came to a head in 373,[34][i] when, according to Faustus and Movses, Pap invited Nerses to dinner at his mansion in the village of Khakh and had him poisoned.
[47][48] Josef Markwart and Hakob Manandian also reject the story of Nerses's poisoning, arguing that Pap would have surely been called to account for it by Basil of Caesarea.
[53] According to Faustus, Pap also demanded control over Caesarea and twelve other Roman cities including Edessa as former Arsacid domains while openly courting Persia, in defiance of the warnings of sparapet Mushegh and other nobles not to break the alliance with Rome.
[55][56] Pap arrived with 300 mounted escorts, but quickly became worried by the absence of the emperor, who was still in Antioch,[22] and therefore fled back toward Armenia and fought off a legion that was sent after him.
[62] Pap married an Armenian noblewoman called Zarmandukht, who bore him two sons: Arshak (Arsaces) III and Vagharshak (Vologases).
[10] Faustus of Byzantium, drawing from epical sources,[66] depicts Pap as totally evil and possessed by demons (dewkʻ) from birth, which caused him to commit sins such as sodomy and bestiality.
[69][40] In Noel Lenski's view, Pap likely struggled to rule a kingdom that was still recovering from the destruction wrought by Shapur II, leading him to make poor decisions that ultimately led to his downfall.