In the same State of Oaxaca are the famous ruins of Mitla, pride of the archaeology of Mexico, situated some thirty miles from the state capital of Oaxaca. These famous ruins of Mitla are of a different character to the pyramidal structures of Monte Alban, although they have a low pyramidal base and were built mainly for religious purposes, it is probable, like most of these prehistoric monuments. They are situated in an inhabited valley, and the ruins consist of five main groups, some of which are exceedingly well preserved. Indeed, whilst the ruins of Mitla are by no means so extensive as others described, they are in the best state of preservation of any in the country. And this is due both to their method of construction and to their environment; for, unlike the low, tropical regions of Chiapas and Yucatan, this district is at a considerable altitude above sea-level. The great "palaces" or halls which these groups form, occupy an area of about 1,800 feet from north to south, by 1,200 feet from east to west. The principal groups are known as the "Hall of the Monoliths or Columns," the "Catholic group," and the "Arroyo group." Like some of the pyramids throughout Mexico, these are oriented, in this case the variation being but a few degrees from the cardinal points of the compass. The remarkable Hall of the Monoliths is a building some 125 feet long by 25 feet wide, with a row of great stone columns running down the centre. These columns are cut from a single piece of trachyte, 15 feet in height, and 3 feet in diameter at the base, tapering somewhat upwards, but of almost cylindrical form, without pedestal or capital. Whilst these columns are intact, the roof, which was doubtless supported on beams resting on the column, is gone. The weight of these monoliths is calculated at five or six tons, and they were cut from quarries in the trachyte rock of the mountains some five miles away, and more than 1,000 feet above the site of Mitla. In this quarry half-cut blocks for columns and lintels are still in place. Food for thought, even for the modern engineer, is this work. [Illustration: PREHISTORIC MEXICO: RUINS OF MITLA; HALL OF THE MONOLITHS OR COLUMNS.]