The people appear to have originated in Ohio. On the southern extremity the works gradually lose their distinctive character, and pass into the higher developed architecture of Mexico; and at the north, north-east, and north-west, the population seem to have been more limited and their works less perfectly developed. The people were preëminently given to agriculture; were not warlike, and only navigated the rivers along their settlements. The fertile valleys of the Scioto, two Miamis, Kanawaha, White, Wabash, Kentucky, Cumberland, and Tennessee rivers were densely populated, as indicated by the numerous works which diversify their surfaces.

The stone and bone implements from the mounds, in their shape differ but little from those of Europe. The hatchets and knives are not only made of flint but also of obsidian, and other hard stones. Copper was the chief metallic substance. Out of this they made various implements, and swords. It was obtained from the shores of Lake Superior, where they carried on extensive mining. In these mines have been found their implements, some of which are very large diorite hatchets, used as sledges for breaking off lumps of copper, and so heavy that it would require more than one man to wield them. The copper was not subjected to heat, but it was hammered cold into such a shape as was desired.

Some idea of the number of the mounds and fortresses may be given from the statement that in the State of Ohio alone there are from eleven thousand to twelve thousand of these works. The fortresses were used for the protection of the people against the predatory warfare of the hostile tribes, or even, it may be, against the incursions made by other Mound-Builders. In regard to the mounds, there has been much speculation, and some archæologists divide them into sacrificial, sepulchral, temple, and symbolical.

Sacrificial.—The sacrificial mounds are characterized by "their almost invariable occurrence within enclosures; their regular construction in uniform layers of gravel, earth, and sand, disposed alternately in strata conformable to the shape of the mound; and their covering a symmetrical altar of burned clay or stone, on which are deposited numerous relics, in all instances exhibiting traces, more or less abundant, of their having been exposed to the action of fire."[88] Among the most remarkable are those found on the Scioto, at the place called Mound City situated on the western bank. The mounds are enclosed by a simple embankment, between three and four feet high. The area occupied is about thirteen acres, and includes twenty-four mounds. One of these is one hundred and forty feet in length, and the greatest breadth is sixty feet. In this mound occurred four successive altars, a bushel of fragments of spear-heads, over fifty quartz arrow-heads, and copper and other relics. The sacrificial deposits do not disclose a miscellaneous assemblage of relics, for on one altar hundreds of sculptured pipes chiefly occur; on another, pottery, copper ornaments, stone implements; on others, calcined shells, burned bones; and on others, no deposit has been noticed. The sacrificial mounds are found at Marietta and other localities.

All the investigations which have been made prove that the altars were not only used for a long period, but also had been repeatedly renewed.

Sepulchral.—The sepulchral mounds are numbered by the thousands. They are simple earth-pyramids, sometimes elliptical or pear-shaped, and vary in height from six to eighty feet. Usually they contain but one skeleton, reduced almost to ashes, but occasionally in its ordinary condition and in a crouching position. By the side of them occur trinkets, and, in a few cases, weapons. These mounds were probably only raised over the body of a chief or some distinguished person.

Temple.—The temple mounds are truncated pyramids, with paths or steps leading to the summit, and sometimes with terraces at different heights. Among the most noted of these is that of Cahokia in Illinois. It is seven hundred feet long at its base, five hundred feet wide, and ninety feet high. Its level summit is several acres in extent.

Symbolical.—The symbolical mounds consist of gigantic bas-reliefs formed on the surface of the ground, representing men, animals, and inanimate objects. In Wisconsin they exist in thousands, and among the devices are man, the lizard, turtle, elk, buffalo, bear, fox, otter, raccoon, frog, bird, fish, cross, crescent, angle, straight-line, war-club, tobacco-pipe, and other familiar implements or weapons.

In Dane county there is a remarkable group, consisting of six quadrupeds, six parallelograms, one circular tumulus, one human figure, and a small circle. The quadrupeds are from one hundred to one hundred and twenty feet long, and the figure of the man measured one hundred and twenty-five feet in length and nearly one hundred and forty feet from the end of one arm to the other. Near the village of Pewaukee, when first discovered there were two lizards and seven tortoises. One of the latter measured four hundred and seventy feet.

In Adams county, Ohio, is the figure of a vast serpent; its head occupies the summit of a hill and in its distended jaws is a part of an oval-shaped mass of earth one hundred and sixty feet long, eighty wide, and four feet high. The body of the serpent extends round the hill for about eight hundred feet, forming graceful coils and undulations. Near Granville, Licking county, Ohio, on the summit of a hill two hundred feet high, is the representation of an alligator. Its extreme length is two hundred and fifty feet, average height four feet; the head, shoulders, and rump are elevated in parts to a height of six feet; the paws are forty feet long, the ends being broader than the links, as if the spread of the toes were originally indicated. Upon the inner side of the effigy is a raised space covered with stones which have been exposed to the action of fire; and from this leading to the top is a graded way ten feet in breadth. On examination it was discovered that the outline of the figure was composed of stones of considerable size, upon which the superstructure had been modelled in fine clay.