The Maya architects did not attempt to handle large masses of stone in the construction of their buildings; no blocks comparable in size with the great lintels of Mitla enter into the composition of Maya temples and in the art of masonry the Maya were far behind the megalithic builders of the Peruvian and Bolivian highlands. The only attempt at stone building, where regularly squared blocks are laid in rows with due attention to the breaking of courses and the bonding of corners, is found at Copan, and that too in only a very small proportion of the ruins of that site. Elsewhere no regard is paid to these two important architectural points, and this fact has contributed in some degree to the downfall of many of the buildings. However, the fault is the less serious owing to the extreme solidity of the stone-and-mortar hearting. As stated above, Maya buildings were faced with a veneer of blocks dressed on the exterior surface; these were usually cut away to some extent behind, so that the mortar in which they were set extended in tongues nearly to the outer face of the wall, just as at Mitla; but in many cases the tenon-like backs of the surface-blocks were not sufficiently prominent, and in consequence they have fallen away from the core of stone and mortar, leaving the latter exposed. This method of facing enabled the builders to ornament their temples with the most elaborate mosaic designs, which are seen in their greatest complexity in Yucatan (Pls. XXIX, 2, and XXX; pp. 350 and 358). The designs here fall roughly into two classes, geometrical patterns, which often appear to be based upon textile art, and grotesque representations of the human face (e.g. Fig. 86, _g_; p. 356). The latter is particularly characteristic of the region, and represents probably the face of the god B, the counterpart of the Mexican Tlaloc, whose nose is frequently prolonged into a regular trunk (see Pl. XXIX, 2). Some of the geometrical patterns are produced by the regular repetition of a small element, and these naturally were easier of construction since they are composed of similarly carved blocks; but many of the designs are formed of blocks each of which has been carved to fit the particular place which it occupies in the whole scheme of ornament, and this fact not only bears witness to a vast amount of patient labour, but implies also that the architect was working in accordance with a definite plan prepared beforehand. In Chichen Itza grotesque masks are found in some of the buildings, composed of details which do not fit into the scheme, a fact which proves that the Maya mason was not above utilizing material gleaned from the ruins of former buildings, besides affording evidence that such structures are of later date. It has already been mentioned that circular columns are peculiar to Yucatan, and it may be added that a variety of ornament derived from them was also applied to the outer surface of buildings, in the form of series of pilasters,