That this remarkable class of earthworks originated in some totally different purpose from the strongholds already described, is obvious. Their site is invariably on a level plateau, and their avenues are connected with the neighbouring flats by laboriously constructed approaches, as if to facilitate the solemn march of processions. The embankments are frequently slight; where a ditch occurs it is generally in the interior; and their whole construction is in striking contrast to the defensive enclosures in their vicinity. At Newark they extend over the level terrace, and, with outlying structures, embrace an area of several miles in extent; while on each side of the Valley, formed by the Racoon Creek, military works occupy prominent elevations presenting special natural advantages for defence. One of those, obviously of a defensive character, encloses the summit of a high hill; but it also contains a small circle with tumuli, covering “altars” corresponding to those hereafter described, which give their peculiar character to the sacred mounds. There is no room, therefore, for doubt that the various works referred to illustrate what may be styled the civil, military, and ecclesiastical structures of the same people, including in the latter public games, such as among many ancient nations constituted one special feature of their religious festivals. One important inference deducible from the peculiar features of the works here referred to, is the state of knowledge of their constructors. The most skilful engineer of our own day would find it difficult, without the aid of instruments, to lay down an accurate square on the scale of some of those described, enclosing an area four-fifths of a mile in circumference. Circles of moderate dimensions might indeed be constructed, so long as it was possible to describe them by a radius; but with such works measuring five thousand four hundred feet, or upwards of a mile in circumference, the ancient geometrician must have had instruments, and means of measuring arcs: for it seems impossible to conceive of the accurate construction of figures on such a scale, otherwise than by finding the angle by its arc, from station to station, through the whole course of their delineation. It is no less obvious from the correspondence in area and relative proportions of so many of the regular enclosures, that the Mound-Builders possessed a recognised standard of measurement; and that some peculiar significance, possibly of astronomical origin, was attached to figures of certain forms and dimensions. [Illustration: FIG. 71.—Cincinnati Tablet.]