The methods of the Maya builder, and in particular his ignorance of the true arch, rendered the construction of an edifice of more than one storey (apart from the roof-comb) a matter of considerable difficulty. Nevertheless buildings of two, and even three tiers of chambers are known, though the plan on which they were erected was extremely wasteful of material and space. Usually the higher or highest tier was supported on a solid construction, around which the chambers of the lower tier or tiers were grouped (Fig. 78). The whole edifice thus resembled in the main a huge stepped mound, with rooms built in each of the steps. Sometimes the outer chambers of a superior tier would overlap those of an inferior to some extent, but in such cases the floor of an upper chamber was almost always supported on the dividing wall of two of the lower. The cave-like structure of Maya buildings is particularly evident in such architectural monstrosities. However, many of the sites do not include buildings of more than one floor (apart from the roof-comb). In some cases, as at Tikal, the upper tiers must have been reached by ladders, as no stairway leads to them, and it is interesting to note in this connection that more than one stela at Piedras Negras represents a god seated in a niche to which a ladder gives access from below (Pl. XX; p. 224). The finest example of a three-tiered building is found at Santa Rosa Xlabpak (Fig. 78), but in this case a broad stairway leads from the ground to the highest tier. Two remarkable buildings of more than one storey call for mention, if only as exceptions to the general rule. These are the square tower at Palenque, and the circular edifice known as the “Caracol” at Chichen Itza. The first (Fig. 75, _f_) had originally at least three floors, as well as two intermediate blind storeys, the chambers of which are grouped around a square core of masonry in which is built a staircase. The second (Fig. 75, _e_), which has two storeys, is constructed round a circular core, in which is a very small spiral stairway. The essentials of construction are the same, the chief differences lying in the facts, firstly, that whereas the chambers of the Caracol are all vaulted, those of the Palenque tower are in some cases furnished with flat ceilings of beams, and secondly, that while the upper storey of the Caracol is considerably less in diameter than the lower, the square tower retains the same diameter throughout. Architecturally the latter is considerably superior to the former, but the shape of the Caracol is interesting since it is the only circular construction now existing in the Maya country, though Landa states that a circular temple to Kukulkan was built at Mayapan, and further remarks that this shape of building was particularly related to this god. It will be remembered that circular temples, according to tradition, were erected to Quetzalcoatl, his counterpart, in Mexico.