The "Coptic period" is an informal designation for Late Roman Egypt (3rd−4th centuries) and Byzantine Egypt (4th−7th centuries). This era was defined by the religious shifts in Egyptian culture to Coptic Christianity from ancient Egyptian religion, until the Muslim conquest of Egypt in the 7th century. The period began in about the 3rd century and, depending on sources and usage, lasted until around the noticeable decline of Christianity in Egypt in the 9th century, or to the arrival of Islam in the 7th century.