Little is known about the life of Leontius Byzantinus. He may have been born around 485 in Constantinople. He joined the heretical Nestorians, but converted and became one of their opponents. He was a monk in Jerusalem and at Constantinople, where he died, possibly around 543. Despite the lack of information about his life, Leontius was an important theologian. He wrote books against heresies, notably those of the Nestorians, Monophysites and Appollinarists, as well as all the known heresies of the time, even the Jews and Samaritans. He defended the title of Theotokos (“God-bearer”) for the Blessed Virgin Mary. He is considered one of the first of the Scholastics.