such as are found at Palenque and Menché, but as a matter of fact the construction is essentially the same throughout. The form of the typical Maya building was to a great extent conditioned by the fact that the primitive architect was ignorant of the principle of the true arch. It is possible that some buildings may have been furnished with flat roofs by means of wooden beams, but if so the beams have decayed and the buildings have fallen in; such structures as have survived were built as follows (Figs. 74 and 77; pp. 323 and 329): The walls, built very thick, were carried vertically up to the desired height, and then the mason commenced to build inwards at a very wide angle, allowing successive courses to overlap, until those on opposite walls approached near enough for the space to be bridged by single slabs. Meanwhile the outer faces of the walls were carried up vertically or at a slope, and the exterior of the roof was finished off flat or with a very slight gable respectively. The distance between the spring of the vault and the apex was considerable, and this gave to the exterior face of Maya buildings a very deep entablature (Fig. 74, _h_) which afforded a magnificent space for ornament. The entablature is separated from the wall proper, which is usually unornamented, by a projecting cornice or “string-course” (Fig. 74, _g_), the design of which varies according to locality, and in some of the Chichen buildings the lower portion of the wall is battered. The form of vault limited the width of the chamber to ten feet or so, but placed no restrictions upon its length, and at Palenque we find long corridor-like chambers, with frequent doorways, built upon this principle. In Yucatan the entablature is nearly always perpendicular (Fig. 74, _h_), at Tikal and Menché it slopes slightly backward, and at Palenque the slope is considerable (Fig. 77; p. 329); but these are inessential details, and it may be said that the typical Maya building is a solid, box-like structure containing a narrow chamber vaulted as described above. Even the more complex edifices are nothing more than an agglomeration of such chambers, and the type holds good for the whole of the Maya region. The nature of the Maya vault embodies the principle, in the words of Spinden, of “the downward thrust of a load on over-stepping stones,” and this thrust was often increased by the addition of a superstructure, usually known as a “roof-comb” (Figs. 74, _l_, and 75, _e_). This addition reached its greatest dimensions at Tikal, where it usually resembles a very high-pitched stepped mound, sometimes solid, sometimes enclosing one or more very narrow blind chambers (Fig. 76, 9, _a_, and 11). The roof-comb was present also at Menché and probably at Naranjo and Piedras Negras (though not at Copan or Quirigua), but attains its greatest artistic development at Palenque (see Pl. XXVII; p. 342), where it is a light and airy structure, pierced with open-work, and elaborately ornamented with