Roman temples usually faced east or toward the rising sun, but the specifics of the orientation are not really understood today; there are notable exceptions, such as the Pantheon which faces north.
Church architecture has evolved over the two thousand years of the Christian religion, partly by innovation and partly by imitating other architectural styles as well as responding to changing beliefs, practices and local traditions. Both theological and practical influences on church architecture have included pagan and secular buildings and those of other faiths. Buildings were at first adapted from those originally intended for other purposes but, with the rise of distinctively ecclesiastical architecture, church buildings came to influence secular ones which have often imitated the architecture of other religions.
During the period of Roman persecution of Christians, most regular worship took place privately in homes. With the victory of the Roman emperor Constantine, Christianity became lawful and then the privileged religion of the Roman Empire. The faith, already spread around the Mediterranean, now expressed itself in buildings. Their architecture was made to correspond to civic and imperial forms, and so the Basilica, a large rectangular meeting hall became the model for churches, with a nave and aisles and sometimes galleries and clerestories. Pagan basilicas had as their focus a statue of the emperor; Christian basilicas replaced the emperor with God as king of heaven. At the east end was placed the altar behind which sat the bishop and his presbyters in an apse.
Tradition has followed therefore that the altar was most often placed at the east end of the church, and by their very design, this would mean that they generally faced east, although from the altar, the priest would effectively be facing west.