Plan of a Western cathedral, with the narthex in the shaded area at the
Floorplan of the
, showing both inner and outer narthex.
The narthex is an architectural element typical of
early Christian and
churches consisting of the entrance or
lobby area, 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.
In early Christian churches the narthex was often divided into two distinct parts: an esonarthex (inner narthex), between the west wall and the body of the church proper, separated from the nave and aisles by a wall,
colonnade, screen, or rail, and an external closed space, the exonarthex (outer narthex),
 a court in front of the church
facade delimited on all sides by a colonnade as in the first
St. Peter's Basilica in
Rome or in the
Basilica of Sant'Ambrogio in
Milan. The exonarthex may have been either open or enclosed, with a door leading to the outside as in the
By extension, the narthex can also denote a covered porch or entrance to a building.