The domestic basilica dedicated as a place of Christian assembly, became with the development of the ecclesiastical system, the Roman _titulus_, the church in the house, and as no public hall was built until after the Peace of the church, these were multiplied as the Christian population grew and numbered 40 by the second century. The Christian basilica was thus in existence and perfected in all its liturgical parts in the first three centuries, and when Constantine built his great extramural churches, he only amplified a type familiar to every Christian. S. Maria Maggiore probably existed as a domestic basilica at a time anterior to that of its reputed founders Liberius and Sixtus, and we know that S. Croce and the Lateran were constructed within the Sessorian palace and the house of the Laterani of which they probably formed the halls. [Illustration: THE COLOSSEUM AT SUNSET Taken from the _Mons Oppius_, one of the two spurs of the Esquiline hill. See pages 5, 11.] Architecturally also the earliest churches resembled more nearly the domestic hall than the public basilica. The latter were little more than a covered portion of the Forum upon which they stood. They were entered from either side through the open ambulatories which as we have seen were free to all. The extremities were walled up later and prolonged into an apse to increase the space available for legal purposes. The domestic basilica on the other hand was a rectangular building roofed and closed on all sides, its single apse at one extremity facing the main entrance. The central space was surrounded on three sides by porticoes dividing it into portions which became the aisles for the worshippers and the narthex for the use of catechumens. The domestic judge's seat standing in the apse was replaced by the bishop's throne, and the _cancellum_ became the chancel rail dividing this portion, the presbytery of the church, from the rest of the building. The ruins of the Flavian basilica in Domitian's house on the Palatine (81-96) affords us a ground plan of such a domestic hall, in this instance placed close to the _triclinium_ of the house and not in a direct line with the _vestibulum_ or entrance as was generally the case. Here a fragment of the _cancellum_ can still be seen _in situ_. The Christian altar of the earliest churches placed in front of the apse, faced the congregation, and a space before it, beyond the depressed portion or _confessio_, was reserved for the choir and was surrounded by a marble balustrade. The columns supported a horizontal architrave, above it a flat wall pierced with windows and the plain roof of cedar-wood beams.