Adaptation of the Basilica
During the Early Christian period (ca. 200-500), the Roman basilica was adopted as the standard design for the Christian church. The basilica (a common type of Roman building) was essentially a large rectangular hall with a gable roof (see roof types). The rear wall of the basilica often featured a semi-circular projection called an apse.12,13
The roof of a basilica is higher over the main hall than the aisles, allowing for clerestories along the upper walls. A clerestory ("clear story") is simply a row of windows set well above eye level, and thus intended purely for lighting.
Large and well-lit, the basilica was ideally suited to activities involving large groups, such as political meetings, legal proceedings, or markets. A facilitator (such as the chairman of a meeting or the judge of a case), if present, might be seated prominently in the apse.7,31
Early churches were physically the same as basilicas; they were simply used for Christian worship rather than the activities listed above. These churches may therefore be described as basilica churches.
Latin Cross and Central Plan
From the Early Christian period onward, the basilica church plan remained a popular option for church architects throughout Europe. Yet the most prevalent church layouts became the Latin cross plan (in Western Europe) and central plan (in Eastern Europe), both of which evolved from the basilica church. The Latin cross design essentially adds two lateral extensions (called "transepts") to the original basilica layout, while the central plan design essentially compresses the basilica into a square (or other shape with rotational symmetry, e.g. octagon, circle, Greek cross).
The central plan church design emerged from an Eastern European fondness for domes; since a dome naturally suggests a central plan building beneath it, the rectangular basilica was compressed into a central plan layout.41 The term "central plan" denotes rotational symmetry: if the plan is rotated around its central point, it looks the same at multiple points of rotation. (Strict rotational symmetry is often slightly violated in central plan architecture.)
Architects developed many variations and embellishments of these two basic layouts. One widespread embellishment of the Latin cross church was the chevet, an extension of the east end in which the aisles form a semi-circular hallway (termed an ambulatory) around the back of the apse, to which a series of additional apses are added. These "extra apses", which may be used as shrines or chapels, are odd in number, thus ensuring a centred apse at the east end of the building.
Standard Church Parts
Traditionally, churches are oriented such that the entrance faces west. The basilica plan may thus be divided into west and east sections.
The west section consists of the narthex (foyer) and nave (where the congregation sits). The roof is higher over the nave than the aisles, allowing for clerestories along the upper nave walls.
The east section consists of the chancel (aka sanctuary) and apse. The chancel, which comprises the remainder of the main hall after the nave, contains the altar and seating for the clergy and choir. The apse is a semi-circular alcove at the east end, often featuring prominent religious sculpture, murals, or stained glass. The line where the nave ends and the chancel begins may be indicated by a railing, though often there is no physical division. The main body of the church (the nave and chancel) is flanked with aisles.
In the case of a Latin cross church, the area where the arms of the cross intersect is called the crossing. A tower (known as the "crossing tower") is often constructed over this area. Each transept of a Latin cross church may be given an altar and/or entrance of its own.
12 - "Roman and early Christian » Early Christian", Encyclopedia Britannica. Accessed May 2009.
13 - "Early Christian art and architecture", Columbia Encyclopedia. Accessed May 2009.
31 - "Basilica", Encyclopedia Britannica. Accessed May 2009.
41 - "Byzantine art", Encyclopedia Britannica. Accessed January 2010.