The extensive works at Aztalan, on the west branch of Rock River, present analogies of a different kind from the sacred and civic enclosures of the Mound-Builders. They constitute, it is believed, the only ancient enclosure, properly so called, throughout the whole region of the emblematic mounds; and, under the name of the “ancient city of Aztalan,” were long regarded as one of the wonders of the western world. Early explorers were on the look-out for the mother city of the Aztecs, and the first surveyor of the earthworks on Rock River named them Aztalan, in the full belief that the long-sought city of Mexican tradition had at length been found. The name was a stimulus to credulity and wonder; and proved the source of much extravagant exaggeration. Walls of brick still sustained by their solid buttresses; a subterranean vault and stairway discovered within one of its square mounds; a subterranean passage, arched with stone; bastions of solid masonry, and other features of the like kind: were all made to correspond with the supposed mother-city of the Aztecs, and the cradle-land of America’s native civilisation. On being subjected to accurate survey, those wondrous features vanish. Freed, however, from exaggeration and falsehood, the Aztalan works still present remarkable characteristics. An area of seventeen acres on the banks of the Rock River is enclosed on three sides by a vallum with regular “bastions,” as they have been termed; although both the construction of the walls, and the site of the enclosure—commanded as it is by elevated land on nearly every side,—preclude the idea of its having been a place of defence. Large, square, terraced mounds occupy the northern and southern angles. In one of them a human skeleton was found; and in others of the mounds coarse pottery occurs; but both may have been deposited long subsequent to the completion of the earthworks of Aztalan. With these exceptions, nothing has yet rewarded the careful and elaborate excavations of its explorers tending to throw light on the original builders. Its bastions have been tunnelled in vain; and cuttings made in some of the largest of a remarkable range of tumuli outside the enclosures revealed only ashes, mingled with charcoal and fragments of human bones, unaccompanied by a single work of art, like those which confer so graphic an interest on the mounds of the Ohio Valley.