This, from the dreaded CE, which affirms Genevra's statement about OSP and others of the era:

The custom of praying with faces turned towards the East is probably as old as Christianity. The earliest allusion to it in Christian literature is in the second book of the Apostolic Constitutions (200-250, probably) which prescribes that a church should be oblong "with its head to the East". Tertullian also speaks of churches as erected in "high and open places, and facing the light (Adv. Valent., iii). The reason for this practice, which did not originate with Christianity, was given by St. Gregory of Nyssa (De Orat. Dominic., P.G., XLIV, 1183), is that the Orient is the first home of the human race, the seat of the earthly paradise. In the Middle Ages additional reasons for orientation were given, namely, that Our Lord from the Cross looked towards the West, and from the East He shall come for the Last Judgment (Durand, Rationale, V, 2; St. Thomas, Summa Theologica II-II:84:3). The existence of the custom among pagans is referred to by Clement of Alexandria, who states that their "most ancient temples looked towards the West, that people might be taught to turn to the East when facing the images" (Stromata, vii. 17, 43). The form of orientation which in the Middle Ages was generally adopted consisted in placing the apse and altar in the Eastern end of the basilica. A system of orientation exactly the opposite of this was adopted in the basilicas of the age of Constantine. The Lateran, St. Peter's, St. Paul's, and San Lorenzo in Rome, as well as the Basilicas of Tyre and Antioch and the Church of the Resurrection at Jerusalem, had their apses facing the West. Thus, in these cases the bishop from his throne in the apse looked towards the East. At Rome the second Basilica of St. Paul, erected in 389, and the Basilica of San Pietro in Vincoli, erected probably in the latter half of the fourth century reversed this order and complied with the rule. The Eastern apse is the rule also in the churches of Ravenna, and generally throughout the East. Whether this form of orientation exercised any influence on the change of the celebrant from the back to the front of the altar cannot well be determined but at all events this custom gradually supplanted the older one, and it became the rule for both priest and people to look in the same direction, namely, towards the East (Mabillon, Museum Italicum, ii, 9). Strict adherence to either form of orientation was, necessarily, in many instances impossible, the direction of streets in cities naturally governed the position of churches. Some of the most ancient churches of Rome were directed towards various points of the compass.

MG