These underground chambers, or _chultuns_, seem to be fairly common throughout Yucatan. Considerable doubt exists as to the uses to which they were put.[34] It seems probable that those the walls of which were plastered with an impervious cement lining were intended as water receptacles, since they could easily have been filled by drainage from the thatched roofs of buildings in the vicinity, which have long since completely disappeared. Though the southern part of Yucatan, unlike the northern, is fairly well watered, plastered _chultuns_ are not infrequently found there, but always situated at considerable distances from a good permanent water supply, as a lagoon or river. The uncemented _chultuns_ would not hold water, and had probably been used as storehouses for corn and other provisions. Some of these chambers were undoubtedly used as burial places, as one at Platon, on the Old River,[35] was covered by a burial mound, and itself contained human bones; but it is possible that their use for this purpose may have been secondary only. The San Andres _chultun_ is somewhat puzzling, as it was certainly not a reservoir for water, nor were any traces of human burial found within it. It had probably been used as a storehouse for food, though it is difficult to understand the object of the oblong shafts, leading into the open air, found at the side of the smaller chamber, as they must have been quite useless for ventilating purposes, not having any opening into the chamber itself through which the air might circulate. MOUND NO. 9 Mound No. 9, situated close to the _chultun_, with three openings, was oval in shape with flattened summit, 44 feet in breadth, 66 feet in length, and 14 feet high at its highest point. On removing the summit of the mound to a depth of about 4 feet the floor of a building, with parts of the walls, was exposed. The cap of the mound, covering the ruins of the building, was composed of blocks of marl, clay, rubble, and limestone. The lower part of the mound, upon which the building stood, was constructed of large blocks of limestone mortared together, forming a solid block of masonry. The building was in a very ruinous condition; as much of its ground plan as could be traced is shown in figure 28. The walls, A, A, A, are 3 feet 4 inches in thickness.