The predominant impression suggested by the great military earthworks of the Mound-Builders is that of the action of a numerous population, co-operating under the guidance and authority of approved leaders, with a view to the defence of large communities. Elaborate fortifications such as that of “Clark’s Work” in the Scioto Valley, or “Fort Ancient” on the Little Miami River, are constructed on well-chosen hills or bluffs, and strengthened by ditches, mounds, and complicated approaches; but the lines of earthwork, like those of the great Scottish hill-forts, are everywhere adapted to the natural features of the site. With the sacred enclosures it is wholly different. Some of these also do, indeed, impress the mind with the imposing scale of their embankments. On first entering the great circle at Newark, and looking across its broad trench at the lofty embankment overshadowed with full-grown forest-trees, my thoughts reverted to the Antonine vallum, which by like evidence still records the presence of the Roman masters of the world in North Britain. But after driving over a circuit of several miles embracing the remarkable group of earthworks of which this is only a single feature, and satisfying myself by personal observation of the existence of parallel avenues which have been traced for nearly two miles; and of the grand central oval, circle, and octagon, the smallest of which measures upwards of half-a-mile in circumference: all idea of mere combined labour is lost in the higher conviction of manifest skill, and even science. The angles of the octagon are not coincident, but the sides are very nearly equal; and the enclosure approaches so closely to a perfect figure that its error is only demonstrated by actual survey. Connected with it by parallel embankments 350 feet long, is a true circle, measuring 2880 feet in circumference; and distant nearly a mile from this, but connected with it by an elaborate series of earthworks, is the circular structure above referred to. Its actual form is an ellipse, the respective diameters of which are 1250 feet, and 1150 feet, respectively; and it encloses an area of upwards of 30 acres.