The era of Constantine, though justly regarded as marking the final disappearance of the last lingering rays of ancient taste, proves yet a most important epoch in the history of architecture. The reception of Christianity as the religion of the empire, not only changed to a very great extent, the entire frame and aspect of society, but in a particular manner influenced the practical art of building. As in the heathen temple was traced the great source of perfection in ancient art, so in the Christian church then established, is to be found the origin of those modes and forms, which, for so many centuries, guided modern practice. But the former structure was one of external magnificence only; internally, it was neither intended, nor, unaltered, adapted, to accommodate large assemblies. In the new religion, this became the primary object in its places of worship: while the early Christians refused to make use of the 'houses of idols.' In this emergency, there remained only one course--to convert the most capacious of unobjectionable buildings into churches. Of all these, the Basilicon presented, not only no difficulties as having been desecrated, but also was directly accommodated to the necessities of the case. The ancient Basilicon was a building of great extent, adjoining the forum or great square, in every city, serving at once the purposes of an exchange for the transaction of business, of a court for the administration of justice, and of a place for general resort. The exterior was adorned with porticoes more or less magnificent, while internally it was separated lengthwise by two or four ranges of columns, into three or five longitudinal divisions, according to its width. Of these, the middle one was the largest, open to the top, and uncovered; the side ones were smaller, roofed in, with galleries opening into the centre compartment, and to which access was had by stairs at the two extremities. Under an arched niche, usually at the extremity of the central division, was a tribunal for the judge, exactly in the situation where the Christian altar was afterwards placed. From the whole description, it is evident, that the only alteration necessary to convert this edifice into a complete church, with its nave and lateral aisles, was to place a roof over the middle portion. Thus the first Christian churches were formed; and hence many of those in Rome still retain the name of Basilicon. Subsequently, the transepts were added, to imitate the cross, though this form seems to have been very early known in the East.