On the Ohio and its tributaries, and farther south, where the mounds are numerous, the inclosures have more regular forms; and in the Ohio Valley very often their great extent has incited speculation. At Newark, Ohio, when first discovered, they were spread over an area more than two miles square, and still showed more than twelve miles of embankment from two to twenty feet high. Farther south, as already stated, the inclosures are fewer and smaller, or, to speak more exactly, the great inclosures and high mounds are much less common than low truncated pyramids, and pyramidal platforms or foundations with dependent works. Passing up the valley, it is found that Marietta, Newark, Portsmouth, Chillicothe, Circleville, Ohio; St. Louis, Missouri, and Frankfort, Kentucky, were favorite seats of the Mound-Builders. This leads one of the most intelligent investigators to remark that “the centres of population are now where they were when the mysterious race of Mound-Builders existed.” There is, however, this difference: the remains indicate that their most populous and advanced communities were at the South. Figure 10 shows a fortified hill in Butler County, Ohio. [Illustration: Fig. 10.--Fortified Hill, Butler County, Ohio.] Among those who have examined and described remains of the Mound-Builders, Messrs. Squier and Davis rank first in importance, because they have done most to give a particular and comprehensive account of them. Their great work, published by the Smithsonian Institution, must be regarded as the highest authority, and those who desire to study the whole subject more in detail will find that work indispensable. EXTENT OF THEIR SETTLEMENTS. Careful study of what is shown in the many reports on these ancient remains seems plainly to authorize the conclusion that the Mound-Builders entered the country at the South, and began their settlements near the Gulf. Here they must have been very numerous, while their works at every point on the limit of their distribution, north, east, and west, indicate a much less numerous border population. Remains of their works have been traced through a great extent of country. They are found in West Virginia, and are spread through Michigan, Wisconsin, and Iowa to Nebraska. Lewis and Clarke reported seeing them on the Missouri River, a thousand miles above its junction with the Mississippi; but this report has not been satisfactorily verified. They have been observed on the Kansas, Platte, and other remote Western rivers, it is said. They are found all over the intermediate and the more southern country, being most numerous in Ohio, Indiana, Illinois, Wisconsin, Missouri, Arkansas, Kentucky, Tennessee, Louisiana, Mississippi, Alabama, Georgia, Florida, and Texas.