When did Priests become Celibate?

Eastern Orthodox priests never did. Many Catholic priests in the middle ages were married and/or had mistresses. They stopped allowing marriage at some point after that. ---- A Catholic Answer The earliest written documentation of celibacy among Catholic priests dates to the fifth century. With the fall of Rome, the barbarian invasions, and general turmoil throughout Christian Europe, the Catholic Church struggled to enforce this discipline throughout the early Middle ages, and succeeded in doing so only later in the Medieval period.