Kivas in the Mesa Verde are always underground and generally circular in shape. The average diameter is 12 to 13 feet and the depth is such that the roof would clear a man's head. At a point about 3 feet above the floor is a narrow ledge running entirely around the room. This ledge is known as the banquette and its exact use is unknown. On this ledge were built six stone buttresses or pilasters, 2 to 3 feet in height, which served as roof supports. Short beams were placed from pilaster to pilaster around the room, and additional series of beams were laid to span the angles formed by the lower series. Normally five or six sets of beams extended this cribwork almost to the ground level. Horizontal beams were then placed across the top and the whole structure was covered with bark and earth. A small square hole in the center of the roof provided an entrance which also served for a smoke vent. On the south side of the kiva the banquette is wider between two of the pilasters than anywhere else around the room. This deep recess is often referred to as an altar, although its exact use is not known. Just back of the wall of this deep recess is a vertical shaft that leads down to meet a horizontal shaft that opens into the kiva just above the floor. This is the ventilator shaft. The fire, burning in the small pit in the center of the room, sent the smoke up through the hole in the roof, and the fresh air was drawn down through the ventilator shaft. Between the ventilator and the fire pit a small wall, known as the "deflector", was constructed to keep the fresh air current from blowing on the fire. Two or three feet from the fire pit, and in a straight line with the ventilator shaft, the deep recess, the deflector, and the fire pit is a small hole in the floor of the kiva. This hole is usually about 3 inches in diameter and from 4 to 6 inches deep; its walls and bottom often covered with a smooth layer of mud. In the present-day kivas this hole is known as the "sipapu", and is considered to be the symbolic entrance to the underworld. The kiva was a combination ceremonial, club, and work room for the men. Even in the present-day villages the women are rarely ever allowed to enter the kivas because of the fact that the men take almost entire charge of the religious work. It is believed that each clan had its own kiva. It may be noted that in almost every case the kiva is surrounded by a group of living rooms. The members of the clan no doubt lived in these rooms and the men held their ceremonies in the adjoining kiva. Two of the kivas in Spruce Tree House have side entrances that lead to nearby rooms. These rooms may have been the homes of the priests, or dressing rooms for them. DATE OF OCCUPATION