Numerous Georgian-Armenian military units participated in the Mongol conquest of Alamut in 1256, where they were personally led by David VII of Georgia.

[17] Meanwhile, Hulagu continued his conquest of the rest of Syria, accompanied by the forces of Hethum I of the Armenian Kingdom of Cilicia and the Crusaders of Bohemond VI of Antioch.

[16][18] The Georgian ruler David VII declined to commit more Georgian-Armenian troops for these Mongol campaigns in Syria, on account that he had suffered huge losses in the 1258 Siege of Baghdad.

[19] Prosh Khaghbakian was involved in the development of the monastery of Geghard in the Kotayk province of Armenia, partially carved out of the adjacent mountain and surrounded by cliffs.

A reliquary with a holy spear bears a dedicatory inscription made by Prince Prosh in 1269: In the year 1269, I, prince Prosh, son of Vasak, inheritor of this divinely prepared holy spear, embellished it with a precious repository to have it intercede for me in the awesome judgment of Christ, and with great hope I donated it to the monastery of Ayrivank‘, the treasured place of my burial, in perpetual memory of me and my children Papak‘, Amir Hasan, and Vasak, and of my consort Dame Khutlu, who passed away in Christ, and of Mkdem and Dame Gohar, who left this world prematurely.He mentions his wife in the inscription, Khutlu Khatun, as well as his children Papak Proshian (died 1298), Vasak (died c. 1268–1273), Amir Hasan I (died 1292),[24] and Mkdem.