But the monolithic columns here are by no means the only remarkable features of the masonry of Mitla. The interior and exterior of these great halls are carved with a beautifully executed geometrical design--the Greek pattern enclosed in a quadrilateral, the blocks upon which they are cut being exactly fitted and adjusted in their places with scarcely visible joints. Indeed, at Mitla, as in other places in the Americas--Huanuco[9] and Cuzco, in Peru, for example--it seems to have been deemed an essential and peculiar art to adjust great blocks of stone with so great a nicety that no mortar was necessary and the joints almost invisible. This, of course, necessitated infinite time and patience--both of which were at the disposal of these prehistoric builders. It is to be recollected, in this connection, that each stone was generally an individual and not a counterpart, and so often had to be fitted to its fellows in the wall, by the laborious method of continually placing and removing. The remarkable and intricate nature of the mosaics and carved blocks at Mitla call forth the admiration of the observer. A vast number of separate stones have been employed, each requiring its respective forming, shaping, and placing, and one of the halls alone shows more than 13,000 such stones in its walls. The stone doorways to these halls are chaste, massive, and effective. The stone lintels in some cases are more than 12 feet long, and nearly 4 feet thick. Indeed, there exist at Mitla nearly a hundred examples of great monoliths, whether columns, lintels, or roof stones, some weighing as much as 15 tons, and up to 20 feet in length. [Footnote 9: See the "Andes and the Amazon."] The earliest account of the ruins of Mitla, by Francisco de Burgoa, a priest of Oaxaca, who visited them in 1674, states that these beautiful halls were the scene, in prehistoric times, of the most diabolical rites. To-day the ruins are surrounded by a rude native population, most of whom dwell in wretched _jacales_, in a waterless and sun-beat valley--an environment in striking contrast to the antique splendour of these halls of the earlier occupiers of the land.