To many of these early churches fine cloisters, that is to say, arcaded colonnades encircling the outer walls, were added, those that once enclosed the ancient basilica of S. Paola fuori le Mura being among the finest still preserved, that may be said to have anticipated the beautiful ambulatories of later monastic and collegiate buildings.
In other cities of the Roman empire are many noteworthy early basilican churches, including S. Apollinare Nuovo within and S. Apollinare in Classe without the walls of Ravenna, the cathedral of Torcello, that is connected by a narthex with the later S. Fosca, in which the transition from the Roman to the Byzantine style is shadowed forth, and the cathedrals of Parenzo and Grado in Istria, the former retaining almost intact its beautiful colonnaded atrium, the latter chiefly remarkable for its fine mosaic pavement.
In addition to the early churches of basilican plan are a few of circular form, such as that at Rome enshrining the tomb of S. Constanza, the daughter of Constantine, dating from about A.D. 354, which has a domed roof and vaulted aisles, the 5th century church of S. Stefano Rotondo in the same town, the latter, though greatly modified in detail, still preserving its two concentric ranges of columns, S. Vitale at Ravenna, and S. George at Salonika, that has a circular nave but an oblong chancel and apse, whilst the 6th century tomb of Theodoric is typical of the use of a similar plan in sepulchral monuments.
In the first centuries of the Christian era it was customary for the ceremony of baptism to be performed in buildings known as baptisteries, apart from, but close to, cathedrals and important parish churches. These buildings were as a general rule of circular or octagonal plan with a tank in the centre of the interior, of size sufficient for the total immersion of candidates. The earliest and also one of the finest existing examples is the Baptistery of Constantino that rises close to S. Giovanni in Laterano, Rome, and is two stories high, with a central domed roof of timber and flat-ceilinged aisles, the massive porphyry columns dividing them from the space set apart for the ceremony of baptism, being surmounted by slender pilasters. Another fine early Baptistery is that at Nocera, which resembles that of Constantine in general plan and style.
The Christians of Egyptian descent, to whom the name of Copts has been given, evolved a style of building that combined with oriental traditions certain details of western architecture. They were very early familiar with the dome, and employed it in churches of a basilican ground-plan even before it was adopted in the Roman Empire. Moreover, certain of the barrel vaults and arches in Coptic places of worship were pointed, so that the most distinctive characteristic of Gothic architecture may be said to have been to some extent anticipated. Except for the effective feature of the dome the exteriors of these buildings were plain and unpretending, but the interiors were in many cases lavishly decorated with marble mosaics. Other peculiarities were the division of the eastern extremity into three semicircular or square recesses, each containing an altar, the use of an elaborately carved screen shutting off the choir or chancel from the nave and aisles, and the introduction of galleries above the latter for the use of the women of the congregation.
Specially noteworthy examples of Coptic architecture are the two churches in Upper Egypt known as the White and Red Convents, the former supposed by some authorities to be even older than the church of the Nativity of Bethlehem, the 6th century church of Dair-as-Sûriâni in the Desert, and the 8th century S. Sergius or Abu Sargah at Cairo, whilst in the oasis of El Bagawat have recently been excavated a large number of sepulchral chapels, dating probably from the 5th century, many of which have domed cupolas greatly resembling in structure those of considerably later Byzantine buildings.
In Syria, as well as in Egypt, are many very interesting early Christian churches, including the vast complex 5th century building at Kalat-Seman dedicated to S. Simeon Stylites, which has four basilicas, each with an apse, grouped about a central octagon; the 6th century church at Sergiopolis; and the smaller contemporaneous ones at Qalb Lorzeh and Roueiha; all of which, though they resemble in general plan the basilicas of Rome, have certain details that appear to shadow forth the characteristics of the Romanesque style, notably in the first the cruciform bays dividing the nave from the aisles, in the second, the use of the lobed arch, and in it and the Roueiha building the grouping of the clerestory windows.
Asia Minor is also rich in examples of early Christian architecture, of which one of the most remarkable is the 5th century S. Demetrius at Salonika, of basilican plan with transepts at the eastern end, nave arcades resembling those of S. Clemente, Rome, and galleries above the aisles, such as those of the Coptic places of worship quoted above. With it must be named the 6th century church in the same city, now used as a mosque, under the name of Eski Djuma, and the considerably later churches at Bin Bir Kilissi that have only recently been explored and are of basilican plan with barrel-vaulted roofing.