The narthex is an architectural element typical of early Christian and Byzantine basilicas and churches consisting of the entrance or vestibule, 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.

Church architecture refers to the architecture of Christian buildings, such as churches, chapels, convents, seminaries, etc. It has evolved over the two thousand years of the Christian religion, partly by innovation and partly by borrowing other architectural styles as well as responding to changing beliefs, practices and local traditions. From the Early Christianity to the present, the most significant objects of transformation for Christian architecture and design were the great churches of Byzantium, the Romanesque abbey churches, Gothic cathedrals and Renaissance basilicas with its emphasis on harmony. These large, often ornate and architecturally prestigious buildings were dominant features of the towns and countryside in which they stood. However, far more numerous were the parish churches in Christendom, the focus of Christian devotion in every town and village. While a few are counted as sublime works of architecture to equal the great cathedrals and churches, the majority developed along simpler lines, showing great regional diversity and often demonstrating local vernacular technology and decoration.