26 ABORIGINAL MONUMENTS
The larger circles are oftenest found in combination with rectangular works, connecting with them directly or by avenues. Some of these are of large size, embracing fifty or more acres. They seldom have a ditch ; but when- ever it occurs, it is interior to the wall. As in the case of the squares or rectangular works with which they are attached, (and which, it is believed, never have ditches, exte- rior or interior,) the walls are usually composed of earth taken up evenly from the surface, or from large pits in the neighborhood. “Evident care seems in all cases to have been exercised, in procuring the material, to preserve the surface of the adjacent plain smooth, and as far as possible unbroken. This fact is in itself almost conclusive against the supposition of a defensive design, especially as we have abundant evidence that the mound-builders understood perfectly the value of the external fosse in their works of defence. The walls of these works are, for the most part, comparatively slight, varying from three to seven feet in height. Sometimes they are quite imposing ; as in the case of ‘the great circle at Newark, Licking county, Ohio, where, at the entrance, the wall from the bottom of the ditch has a vertical height of not far from thirty feet. The square or rectangular works attending these large circles are.of various dimensions. It has been observed, however, that certain groups are marked by a great uniformity of size. Five or six of these now occur to the writer, placed at long distances asunder, which are exact squares, each measuring one thousand and eighty feet side—a coinci- dence which could not possibly be accidental, and which must possess some significance. It certainly establishes the existence of some standard of measurement among the ancient people, if not the possession of some means of deter- mining angles. The rectangular works have almost inva- riably gateways at the angles and midway on each side, each of which is covered by a small interior mound or ele- vation. In some of the larger structures the openings are
