Babai the Great ( , c. 551 – 628) was an early church father of the Church of the East. He set several of the foundational pillars of the Church, revived the monastic movement, and formulated its Christology in a systematic way. He served as a monastic visitor and coadjutor with Mar Aba as unofficial heads of the Church of the East (often called the "Nestorian Church" by those in the West) after Catholicos Gregory until 628 AD, leaving a legacy of strong discipline and deep religious Orthodoxy. He is revered in the modern Assyrian Church of the East. Biography Babai the Great (not to be confused with Mar Babai I, the first autonomous leader of the Church of the East) was born in Beth Ainata in Beth Zabdai, on the west bank of the Tigris, near Nisibis. He was born to a family of humble means, and studied at the Christian School of Nisibis under the directorship of Abraham of Beth Rabban. Sometime around 571 A.D., when the Origenist Henana of Adiabene became the new headmaster, Babai's teacher, Abraham the Great of Kashkar, founded a new monastery on Mt. Izla above Nisibis. Babai taught for a while at the Xenodocheio of Nisibis. After that he joined the newly founded monastery of Abraham on Mt. Izla. When Abraham died in 588, Babai left and founded a new monastery and school in his home country Beth Zabdai. In 604 Babai became the third abbot of Abraham's monastery on Mt. Izla. Abraham the Great had started a monastic reform movement which Babai and other disciples carried through. Since Bar Sauma and the Synod of Beth Lapat, monks and nuns had been encouraged to marry. When Babai returned to Mt. Izla in 604, he expelled monks that lived with women on the fringes of the monastery, and enforced strict discipline, emphasizing a deep life of prayer and solitude. The result was a mass exodus, not only of the married monks. But the Church of the East was with Babai. In 604, the Catholicos Mar Sabrisho I died and a new Catholicos had to be elected. The choice fell between two men named Gregory: Bishop Gregory of Nisibis and Professor Gregory of Seleucia. King Khosrau II, ruler of the Sassanid Empire, stated only that his preferred candidate was Gregory, possibly meaning the bishop. The king's influential wife Shirin, however, disliked Gregory of Nisibis and