In Byzantine architecture, the outer narthex beyond a church’s inner vestibule is called an exonarthex.
The exonarthex is an additional entrance zone placed outside the esonarthex, or inner narthex. It could form part of the approach to a church and might contain passages, chapels, tombs, or spaces connected with processions and worship.
This layered entrance arrangement was especially common in Byzantine monastic and large ecclesiastical complexes. The narthex itself stands between the church interior and the exterior, while the exonarthex extends that transitional sequence outward.
The term is sometimes used loosely in descriptions of church façades, so plans and architectural context matter. It should not be confused with the atrium, an open courtyard that could precede some early Christian basilicas, or the bema, which belongs to the sanctuary area.