The narthex is an architectural element typical of early Christian and Byzantine basilicas and churches consisting of the entrance or vestibule, located at the west end of the nave, opposite the church's main altar. Traditionally the narthex was a part of the church building, but was not considered part of the church proper.

The royal doors, holy doors, or beautiful gates are the central doors of the iconostasis in an Eastern Orthodox or Eastern Catholic church. The sanctuary is separated from the nave by a wooden screen called the iconostasis. The iconostasis represents Christian continuity from the veil of the Temple in Jerusalem which separated the people from the Holy of Holies that housed the Ark of the Covenant. Normally, the iconostasis has three doors in it. The two single doors to the right and left are called "deacons' doors" or "angel doors" and they usually have on them icons of either sainted deacons or the Archangels Michael and Gabriel. These are the doors that the clergy will normally use when entering the sanctuary. The central double doors are the "holy doors", which are considered to be most sacred, and may only be entered at certain sacred moments during the services, and only by ordained clergy.