thumb|right|Map of the Diocese of Egypt in antiquityThe diocese of Ammonia (Latin: Dioecesis Ammoniacensis|link=no) is a suppressed and titular see of the Roman Catholic Church.[1] It is all that remains of the ancient bishopric that was centered the Siwa Oasis during late antiquity,[2] when it was in the Roman province of Marmarica and suffraged by the archdiocese of Darni. Today Ammoniace survives as a titular bishopric and has been vacant since January 24, 1983.[3]