The purpose of the tank is suggested by certain of the stucco reliefs on the outside of the enclosing wall. In the gable, above the entrance, is a vase, standing out from a blue ground, with a kneeling figure on either side. The frieze contains Egyptian priests and priestesses, also on a blue ground, with their faces turned toward the vessel (Fig. 82). The figures are all worshipping the sacred water in the vase. [Illustration: Fig. 82.--Part of the façade of the Purgatorium.] Of the other figures in relief, only the two goddesses in the panels at the sides of the entrance have an Egyptian character. Under each of them was a small altar of tufa, attached to the wall; the figure at the left (Fig. 82) is plainly Isis. The side walls are decorated with reliefs in Greco-Roman style. They are divided into a large middle panel, containing two figures, and two side panels, each with a Cupid. In the middle panel, on the right side, Mars and Venus are represented; in that at the left, Perseus rescuing Andromeda (Fig. 83). The dwelling back of the colonnade, on the south side, consists of a kitchen (8), a dining room (7), a sleeping apartment (9), and two small rooms at the rear, under the stairway leading to the highest seats of the Large Theatre. The ritual of the Egyptian gods was so exacting, and the services of worship were so numerous, that it was necessary for one or more priests to reside within the precincts of the temple. These rooms were the habitation of a priest. [Illustration: Fig. 83.--Decoration of the east side of the Purgatorium--Perseus rescuing Andromeda. At the right and the left floating Cupids, the one at the left bearing a box of incense.] One of the rooms on the west side (6) is oblong in shape, with five broad, arched entrances opening from the colonnade. The walls were richly decorated in the last Pompeian style. There were seven large paintings, five of which were landscapes with shrines, part being Egyptian landscapes; the other two represent Io watched by Argus, with Hermes coming to rescue her, and Io in Egypt, received by Isis. Against the rear wall was a pedestal, on which probably stood the female figure, above life size, the remains of which were found in one of the entrances. Only the head, the hands, and the front parts of the feet were of marble; the rest was of wood, no doubt concealed by drapery. The priests seemingly had started to carry the statue with them when they fled, but abandoned the attempt at the doorway. In the same room a marble table, a sistrum, two pots of terra cotta, three small glass bottles, and a glass cup were found. We may safely conclude that here the common meals were served, of which, as we learn from Apuleius, the devotees of the cult partook. And when, in connection with the great festivals, the Mysteries were celebrated with a presentation of the myth of Isis and Osiris in pantomime, this large room was well adapted for the sacred exhibitions.