thumb|right|Map of the Diocese of Egypt in antiquityThe Diocese of Zagylis is the titular diocese of the Roman Catholic Church,[1] established in 1933 by Pope Pius XI, named after the ancient city of Zagylis in present-day Libya.[2] This city was in the Roman province of Libya Inferior.[3] Since the foundation, the diocese had no titular bishop.[4]
The diocese re-establishes an ancient bishopric that flourished in the Roman Empire.[5] Three bishops from antiquity are known.[6]