From Monachos.net
Leo the Great of Rome (d. 461)
- Pope Leo's most significant contribution to the Christological discussion was certainly this great letter, written to his brother-bishop Flavian, yet intended for the Church at large and known throughout history as the Tome of St Leo. Unable personally to attend the Fourth Ecumenical Council (Chalcedon, AD 451), Leo nonetheless wished his voice to be heard on the matters that had been under consideration prior to its convening. The text of this Tome played a formative role in the deliberations of the Council.