1) Propylaeum- the entrance building of a sacred precinct, whether church or imperial palace.
2) Atrium- in early Christian, Byzantine, and medieval architecture, the forecourt of a church; as a rule enveloped by four colonnaded porticoes.
3) Narthex- the entrance hall or porch proceding the nave of a church.
4) Nave- the great central space in a church. In longitudinal churches, it extends from the entrance to the apse (or only to the crossing if the church has one) and is usually flanked by side aisles.
5) Side Aisle- one of the corridors running parallel to the nave of a church and separated from it by an arcade or colonnade.
6) Crossing- the area in a church where the transept and the nave intersect.
7) Transept- in a cruciform church, the whole arm set at right angles to the nave. Note that the transept appears infrequently in Early Christian churches. Old St. Peter's is one of the few example of a basilica with a transept from this period. The transept would not become a standard component of the Christian church until the Carolingian period.
8) Apse- a recess, sometimes rectangular but usually semicircular, in the wall at the end of a Roman basilica or Christian church. The apse in the Roman basilica frequently contained an image of the Emperor and was where the magistrate dispensed laws. In the Early Christian basilica, the apses contained the "cathedra" or throne of the bishop and the altar.
9) Nave elevation- term which refers to the division of the nave wall into various levels. In the Early Christian basilica the nave elevation usually is composed of a nave colonnade or arcade and clerestory.
10) Clerestory- a clear story, i.e. a row of windows in the upper part of a wall. In churches, the clerestory windows above the roofs of the side aisles permit direct illumination of the nave.