In the basin of the Mississippi, particularly in that portion lying east of the great river, there are numerous mounds which were reared by human beings, apparently in very early times, before American history begins. They are found most frequently upon the banks of lakes and rivers, and often upon the summits of high bluffs overlooking the country. No attempt has ever been made to count them, for they could be numbered by tens of thousands; in the small county of Trempealeau, Wisconsin, for instance, over two thousand have been found by surveyors. Most of the mounds have been worn down, by hundreds of years of exposure to rain and frost, till they are but two or three feet in height; a few, however, still retain so majestic an altitude as eighty or more feet. The conical mounds are called by ethnologists tumuli. Other earthworks are long lines, or squares, or circles, and are probably fortifications; some of the best examples of these are still to be traced at Aztalan, Wisconsin. In many places, especially in Ohio and Wisconsin, they have been so shaped as to resemble buffaloes, serpents, lizards, squirrels, or birds; and some apparently were designed to represent clubs, bows, or spears—all these peculiarly shaped mounds being styledeffigies. The mounds attracted the attention of some of the earliest white travelers in the Mississippi basin, and much was written about them in books published in Europe over a hundred years ago. Books are still being written about the mounds, but most of them are based on old and worn-out theories; those published by the Ethnological Bureau, at Washington, are the latest and best. Many thousands of these earthworks have been opened, some by scientists, many more by curiosity seekers, and their contents have, for the most part, found their way into public museums. Many of the mounds have been measured with great accuracy, and pictures and descriptions of them are common. Until a few years ago, the opinion was quite general, even among historians and ethnologists, that the mounds were built by a race of people who lived in the Mississippi basin before the coming of the Indians, and that the mound builders were far superior to the Indians in civilization. Many thought that this prehistoric race had been driven southward by the Indians, and that the Aztecs whom the Spaniards found in Mexico and Central America four hundred years ago were its descendants. We have in Wisconsin a reminder of the Aztec theory, in the name Aztalan, early applied to a notable group of earthworks in Jefferson county.