An orthodox church is, in general, divided into three rooms, counting from the east: the bema, the naos and the narthex. The bema, or sanctuary, is the holiest room, while the narthex is the least sacred of all. However, there are churches that have a further architectural volume in front of the narthex. Varying in structure and shape, from an open portico to a closed room, this fourth architectural unit, more or less integrated in the church building, is usually called the exonarthex. It is clear from the rich literature on orthodox church architecture that the term exonarthex is used as a denomination for all the kinds of building units that are situated in front of the narthex.

The present thesis aims firstly to define these "additional" building units and then to demonstrate the ways in which they have spread both over time and geographically. The different types of these architectural structures are discussed; in certain cases they were built at the same time as the church, while in others they were added later. The research analyses a period of eight hundred years, from the 9th century to the end of the 16th. Geographically it encompasses the region known today as the Balkans, but some of the comparative analyses refer also to Russian and Caucasian architecture.

Until now, the term exonarthex has been used in a general and rather imprecise way. The second major question addressed by this thesis is to answer whether this term is meaningful. And if it is, what does it mean? The aim is to find out if it is possible to identify similar architectural features and functional characteristics for a whole group of monuments, not only for the palaiologan churches of Constantinople and Thessaloniki, but also for a large number of buildings from later periods and from other orthodox regions.

In order to reach a correct definition of the exonarthex we must therefore consider the relationship existing between the room itself and the inner or outer parts of the church in terms of a balance between the theological and the practical. The more the room opens towards the outside world the less its religious importance becomes, although the latter does not disappear completely. The majority of exonarthexes are sizeable architectural volumes which open through large windows or arcades. Light, which plays a central role in the theological doctrine of the time - the hesychasm - appears to have been used as a means of architectural expression, to concretize and even emphasize, in a pleasing way, the strong link between the sanctified inner space of the church and the secular world around. The daylight flowing into the exonarthex transforms this first room of the church into a kind of intermediate zone in front of the half-lightened narthex.

During the palaiologan renaissance, theologians appear to have used architecture to emphasize that the individual now has freer access to the House of God, and, perhaps more important, that the Divine and Man should leave the church together, because "Man's task is to sanctify the world, not to get away from it" (Zernov). The more humane content of religion offered new impulses to church building and gave master-builders additional opportunities to further develop the architectural heritage of antiquity in accordance with the new direction of the religious message - from the interior of the church to the world surrounding it.