The military works of the Mound-builders, other than those previously mentioned as existing on the Lakes and in Western New York State, are of a twofold character, consisting first of fortified eminences, of which an instance is found in Butler County, Ohio, where 16³⁄₁₀ acres are walled in on the summit of a hill, and the entrance to the enclosure guarded by a complicated system of covered ways. On Paint Creek, Ross County, a remarkable stone work encloses 140 acres, in the centre of which was an artificial lake, probably to supply water in case of a siege. Perhaps the most remarkable fortification left by the Mound-builders is that known as Fort Ancient, Ohio, on the Little Miami River, forty-two miles north-east of Cincinnati. The specialist is already familiar with the oft-quoted description of the Survey by Prof. Locke, made in 1843. We will therefore only refer to a few of the measurements contained in that description. “The work occupies a terrace on the left bank of the river, two hundred and thirty feet above its waters. The place is naturally a strong one, being a peninsula defended by two ravines, which, originating on the east side, near to each other, diverging and sweeping around, enter the Miami, the one above, the other below the work. The Miami itself, with its precipitous bank of two hundred feet, defends the western side.” * * * “The whole circuit of this work is between four and five miles. The number of cubic yards of excavation may be approximately estimated at 628,800”. The embankment stands in many places twenty feet in perpendicular height. The most interesting and valuable paper on this work is that by Mr. L. M. Hosea, of Cincinnati, in the _Quarterly Journal of Science_ (Cincinnati), October, 1874, p. 289 _et seq._ This writer observes that it has often been remarked that the form of Fort Ancient resembles a rude outline of the continent of North and South America. None of the mounds contained in the enclosure have yielded any relics of special interest. The greatest possible diversity of opinion exists concerning the antiquity of the abandonment of the works. Judges Dunlevy and Force, the latter in his memoir on the _Mound-builders_,[33] estimate the period as a thousand years, while Mr. Hosea thinks several thousand years would be required to produce the numerous little hillocks and depressions which mark the spot where trees have grown, fallen and decayed. Reasoning from other data, we are inclined to the more conservative opinion of Judge Force as altogether the safer. Fort Ancient, which could have held a garrison of 60,000 men with their families and provisions, was one of a line of fortifications which extend across the State and served to check the incursion of the savages of the North in their descent upon the Mound-builder country.