This group has been described several times by explorers, whose accounts have differed considerably in value. The most important of these are the descriptions and drawings by Dupaix and Castañeda, made in 1806, and the description and valuable photographs by Charnay, the latest explorer of this group, whose work was performed in 1859.[520] The mitla ruins are distributed into four groups of buildings (generally called palaces or temples) and two pyramids. The principal edifice is described as follows: three low oblong mounds only six or eight feet high but surmounted by stone buildings, enclose a court. The court measures 130 by 120 feet. The eastern and western buildings are in a fallen and ruined condition. The northern building, however, presents a singular example of ancient grandeur. The southern portion measures 36 by 130 feet, and the northern 61 feet square. The edifice is about eighteen feet high, having walls varying from four to nine feet in thickness. The accompanying cut, a photographic reduction of Charnay’s photograph, gives a correct idea of the western façade of the northern building.[521] The walls of this edifice are constructed in a somewhat novel manner, their interior portions being nothing more than clay intermixed with stones, thus furnishing a poor substitute for the cement and stone filling in the inner parts of Yucatanic walls. However, the exterior facing of the walls is of hewn stone blocks cut in different forms and sizes, and so set in relation to each other as to present examples of perhaps the finest variety of grecques found in any structure in the world.[522] Two layers of large stone blocks form the base of the palace, from which rises buttresses and a framework of stone, filled in with panels of mosaic, in patterns as described. We pronounce these grecque patterns mosaics, because of the manner of their structure. They are not of the nature of sculpture, since each pattern, with all its regularity, is composed of small brick-shaped blocks of stone built into the wall, mosaic-like, thus forming the graceful patterns shown in the cut. No trace of mortar has been found at Mitla. The inner surface of the wall in the northern building was smoothly plastered without any ornament. Six round stone columns standing in line occupy the centre of the apartment, and no doubt supported a roof of wood or stone, but more probably of the former.[523] The cut in Baldwin’s work, copied by Bancroft showing the interior of the apartment and the six columns, conveys an incorrect impression as to the form of the columns and the character of the walls, as is proven by Charnay’s photograph.[524] The façades of the inner court of the northern wing of the palace are finished with mosaics of great beauty. Four or five feet of the wall is plain at the bottom except that the plastering was evidently frescoed in various colors. The remainder of the wall is decorated with