For the first three centuries after the birth of Christ the early Christians suffered much persecution and martyrdom. The new religion was ridiculed and despised, and the converts of the new faith were obliged to hold their meetings and to worship in secret, which they did in the narrow but extensive catacombs in which they secretly buried their dead. The catacombs are found chiefly in the neighbourhood of Rome and Naples, and are cut in the dark soft tufa stone, in the nature of long passages, winding and doubling in their labyrinthine twistings. Some of these passages are so narrow as to barely admit of one person to pass in height or width. On either side of these narrow ways are cut out openings just large enough for the bodies of deceased persons to be deposited. The body of the deceased was thus thrust into the narrow tomb, and with it was buried a flask of sacred oil. The entrance was then closed with a stone, on which would be engraved the name or initials of the dead. Some of the catacombs were hollowed out in places into lofty and capacious chambers and niches. These were used as chapels for the early Christian worship, the walls and ceilings of which were decorated with paintings of a very primitive character. The more important of these catacombs in which chapel-like rooms are found are those of S. Calisto, S. Sebastiano, S. Lorenzo, and S. Agnese, at Rome; and at Naples those of S. Mario della Sanita, S. Gennara de Poveri, and S. Maria della Vita. Constantine became Emperor of the Romans (A.D. 312-337), and in the course of his reign embraced, or professed, Christianity, and proclaimed it the state religion. After this event freedom was allowed the converts of the new faith to celebrate their love-feasts in a public and open manner. It was found difficult all at once to provide the necessary buildings for this purpose, and we hear of the heathen temples and great halls of the Roman baths being used as Christian churches—the Pantheon at Rome was used for this purpose—but few of these buildings were large enough or of the right shape to hold large masses of the faithful, and at the same time to provide for the celebration of the worship by the bishops and priests in presence of the congregation, besides the objection of having the odour of heathenism still clinging to them. The supposed model for the early Christian churches was found in the halls of justice and commerce of the Roman times. It is doubtful, however, whether the early Christian architecture owed so much to the basilica form of justice halls as has been so generally supposed. The general plan of the basilica churches was rectangular, with a semicircular portion added to the back, as the plan of the apse; in the front was the atrium, a free quadrangular fore-court surrounded with pillars. This was usually roofed on the four sides, with an opening in the centre, like the atrium of a Roman house.