These mounds are distinguished by their great regularity of form and general large dimensions. They occur most usually within, but sometimes without, the walls of enclosures. They consist chiefly of pyramidal structures, truncated, and generally having graded avenues to their tops. In some instances they are terraced, or have successive stages. But whatever their form, whether round, oval, octangular, square, or oblong, they have invariably flat or level tops, of greater or less area. Examples are known in which, although but a few feet in elevation, they cover several acres of ground; in which cases they are commonly called “platforms.”
Mounds of this class are not numerous in Ohio, and it is believed are only found at Marietta, Newark, Portsmouth, and in the vicinity of Chillicothe. These are all described, and their predominant features illustrated, in the accounts of the works at the several points where they occur, to which attention is directed. (See Plates XVIII, XXV, XXVI.) Those at Marietta are situated within an enclosure; those at Newark and near Chillicothe, in close connection with small circles upon which they seem to have some degree of dependence. So far as ascertained, they cover no remains, and seem obviously designed as the sites of temples or of other structures which have passed away, or as “high places” for the performance of certain ceremonies. The likeness which they bear to the «Teocallis» of Mexico is striking, and suggestive of their probable purposes.
In addition to the pyramidal structures here noticed, there are others somewhat [p174] different in their forms, but which were undoubtedly appropriated to the same purpose. The mound embraced in the circular work connected with the Portsmouth group, is an example. (See Plate XXVIII.) Though much defaced, its original plan can easily be made out. It is circular, placed on a terrace, is truncated, and has a spiral pathway leading to its summit. The purpose already assigned to it, viz. that of a site for a temple, or a “high place” for the performance of ceremonies probably connected with the superstitions of the ancient people, is indicated not less by the peculiarities of its construction, than by the character of the enclosure in which it is situated.