| Cyriacus I of Byzantium | |
| Patriarch Of: | Bishop of Byzantium |
| Enthroned: | 217 |
| Ended: | 230 |
| Religion: | Early Christianity |
Cyriacus I (Greek: Κυριακός; died 230) succeeded Philadelphus as Bishop of Byzantium and governed the local church for 13 years. In some catalogues appears under the name Cyrillianus.