The wilderness monastery of St Gregory of Sinai suffered often from robbers. The abbot sent St Theodosius to the emperor Alexander with a request to defend the monastery. The pious Bulgarian Tsar, at the request of the ascetic, provided him with the means to surround the monastery with strong walls with towers, and made the monastery secure with land and cattle.
During his final journey to Trnovo on an errand for the abbot to the Tsar, a nobleman asked St Theodosius to take him along to the monastery. The holy ascetic brought him to St Gregory of Sinai. This was Romanus, who became the sincere and beloved disciple of St Theodosius.
After the death of St Gregory of Sinai (November 27, 1347), St Theodosius refused to become head of the monastery, and he left the monastery with his disciple Romanus for solitary struggles. They founded a monastery on a hill near Trnovo, afterwards called Theodosiev.
In 1360, St Theodosius became grievously ill. Wishing to see his friend St Callistus once more, he went to him at Constantinople, entrusting the direction of the monastery to his disciple Romanus.