In 591, Emperor Maurice had subjected Armenia to a second partition, whereby 60 percent of the country was put under control of Byzantium and the remainder under the control of Persia. Thus Armenia became severely destabilized at the beginning of the seventh century. The Arab invasions began in 640, ushering in two more centuries of political turmoil and devastation. The conquest of Armenia by Persia had been speedy, but it took the Arabs half a century to subjugate the country. The first raid was aimed at the capital, Dvin, which the Arabs sacked and destroyed. The Byzantine general, Procopius, who had been charged with the responsibility of defending the country, was defeated. The nakharar Theodore Rshtuni, however, heading a united Armenian force, succeeding in resisting the Arabs until 644 and was named commander in chief of the Armenian army by Constans.
In 650 a large army was sent by the Arab governor of Syria, Mua'wiya, penetrating most of Armenia. Rshtuni could depend on neither Persia nor Byzantium for help because the Persian Sassanid Empire had collapsed before the Arab conquest of Armenia began and Byzantium continued to demand acceptance of the canons of Chalcedon as a precondition to assistance. In fact, Byzantine pressure was so strong that Catholicos Nerses III Shinogh (the Builder, 641-61) and Rshtuni felt impelled to convoke a church council at Dvin in 648, which rejected the conditions imposed by Byzantium. The only choice left for Rshtuni was to risk making peace with the Arabs. The truce, signed in 652, included conditions Armenia felt quite tolerable: Constans II was forced to surrender Armenia to the Arabs, who granted her virtual autonomy and appointed Rshtuni ostigan (governor)....
In 654, however, with the sudden death of Rshtuni and the looming crisis in the caliphate, which resulted in the split between the Sunni and Shiite sects in 656, provided an opportunity for Byzantium to reassert power over Armenia. The Armenian nakharars of the time were also divided in their loyalties and were exploited by both sides. Rshtuni's successor, Hamazasp II Mamikonian [655-658], sided with the Byzantines, but in 661 Arab suzerainty was reestablished. 1
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In Theophanes AM 6143 he is called πασαγνάθης...
A member of the Armenian dynastic family of the Rshtuni, he is often alluded to as 'Lord of the Rshtunis' (Sebeos xxviii, p. 87, xxx, p. 101, xxxii, pp. 107-8, xxxv, pp. 133, 138, xxxviii, p. 145. Father of Vard... Father-in-law of the Mamikonian Hamazasp; Sebeos xxxv, p. 138.
He was brought up at the Persian court under Chosroes II Parwez, together with Varaztiroch; Sebeos xxxii, pp. 106-7.
He became ishkhan (ruler) of the Canton of the Rshtuni (near Lake Van); Sebeos xxix, p. 94. In 628 he proposed Christopher, a religious with Rshtuni connections, to succeed Comitas as catholicus of Armenia; Sebeos xxviii, p. 87. In 632/633 he attended the council of Theodosiopolis; Narr. de reb. Arm. 121, and see Tournanoff, Traditio, x, p. 156, n. 202. In 638, when disturbances occurred over the overthrow of David Saharuni, he is said to have maintained his troops in good order and preserved several cantons from trouble; Sebeos xxix, p. 94.... 2
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