As Arsaces III and his younger brother, Vologases, were both too young to rule and succeed their father, the Roman emperor Valens had sent their paternal first cousin Varasdates (Varazdat) to occupy the Armenian throne.
Their cousin who was a young man highly reputed for his mental and physical gifts had lived in Rome for an unknown period of time.
In 378 with the failed reign of Varasdates and the murder of Mushegh Mamikonian, who was Vardandukht’s paternal uncle, her father, Manuel[5] filled his late brother’s position of sparapet.
Manuel raised Arsaces III and his brother Vologases to the throne as co-kings of Armenia, under the nominal regency of their mother Zarmandukht.
From this invasion, the authority of Arsaces III became lessened as he only maintained Western Armenia,[14] in which his small kingdom was of a line from Erzurum to Mush.