The Three Holy Ierarches ( Greek: Οἱ Τρεῖς Ἱεράρχες ) of Eastern Christianity refers to Basil the Great (known as Basil of Caesarea), Gregory the Theologian (known as Gregory of Nazianzus) and John Chrysostom. They were highly influential bishops of the early church who played pivotal roles in shaping Christian theology. In Eastern Christianity they are also known as the Three Great Hierarchs and Ecumenical Teachers, while in Roman Catholicism the three are honored as Doctors of the Church. The three are venerated as saints in Eastern Orthodoxy, Catholicism, Anglicanism and other Christian churches. All three have separate feast days in January: Basil on January 1, Gregory on January 25, and Chrysostom on January 27. A January 30 feast day commemorating all three in common was instituted around the year 1000.