The method of construction of the primitive churches, however, according to the liturgical regulations of the period, is still an obscure question, and one surrounded with uncertainty. It has been surmised, with much probability, that the subterranean chapels of the catacombs of Rome were the models of the first churches; and such is the opinion of the most learned archæologists. It was from the very depths of these sepulchral caverns that Christian art, bursting forth into open day after the long series of persecutions, built its crypts and its churches after the types of its hidden shrines, at first in the transmural cemeteries, and afterwards, towards the end of the third century, in the midst of the Christianized populations and in the very centre of their cities. In 303, the date of the decree of Diocletian closing the Christian places of worship, there were already forty churches and chapels in Rome. The shape of these primitive sanctuaries is not well known; they were probably in general of one uniform pattern, specially adapted to the liturgical ceremonies of the day, though considerations of safety, the capabilities of the site, and other imperious necessities, no doubt frequently obliged their architects to depart from precedent and to vary the character of their construction. It was not until the reign of Constantine that Christian edifices began to assume the attributes of size, magnificence, and majestic boldness of outline. It was then that the emperor erected basilicas in the interior of his Lateran and Vatican palaces for the first time, and consecrated to the worship of the true God those immense edifices in which art was the humble handmaid of religion and bathed itself in the ineffable splendours of the faith. The crypts or chambers (_cubicula_) of the Catacombs were reproduced in the full light of day in the early churches; they were of a quadrilateral shape, with three arched naves, and three vaulted recesses (_arcosolia_) which served at once as tombs for the holy confessors and shrines for the celebration of the eucharist. These sanctuaries were generally of greater length than breadth, after the analogy of the ship or vessel (_navis_), this mysterious symbolism finding favour with the early Christians. [Illustration: Fig. 179.--Church of St. Antony, Padua, completed in 1307; the seven cupolas were added in the Fifteenth Century. The bronze equestrian statue which stands in front of the church was executed in 1453 by Donatello, and represents the famous captain, Gattemalata.] [Illustration: Fig. 180.--Foot of a large Choir Candelabrum in gilt bronze, with seven branches, nineteen feet high, and known as the “Tree of the Virgin,” because one of its ornaments represents the Infant Jesus adored by the Magi, in the arms of the Virgin.--Work of the Thirteenth Century, in Milan Cathedral.]