Small clay lamps adorned with Christian symbols have been found in numbers in all Christian centers, especially in the Roman Catacombs. They may be divided into two classes: lamps of the classic period, before Constantine, which are round with an ascending perforated handle, of workmanship superior to those of the later period; those of the Constantinian epoch which are boat-shaped with an unperforated handle running to a point. Lamps of bronze have also been found, sometimes patterned after symbolic animals. The early Christians used lamps from necessity; a burning lamp before the Blessed Sacrament is now obligatory.