COSTANTINO I. — Armenian Katholikós, born in 1220, died on 9 April 1267, known as Bartarberdtzi, and praised by his contemporaries as a virtuous and wise man. He had the merit of convening the Armenian Synod of Sis in 1242, whose Acts he transmitted in an encyclical letter to the Eastern Armenians, where they were accepted; he sent Pope Innocent IV the orthodox faith of the Armenians concerning the procession of the Holy Spirit, and in 1245 also his own profession of faith. With the Greeks he agreed on the Chalcedonian Christological formula.
In the latter part of the thirteenth and fourteenth centuries there were three other Armenian katholikói of the same name, who should not be confused with one another.
BIBL.: Brosset, Deux historiens arméniens, Kirabos de Gaud-zac, Oubhtanés d'Ourba, Pietroburgo 1870; Armenian ed., Venezia 1865; F. Tournebize, Hist. politique et religieuse de l'Arménie, I, Parigi 1910, pp. 285–98. Garabed Amaduni