The greatest concentrations of mounds are found in the Mississippi and Ohio valleys. Although the name mound builders implies homogeneity, most archaeologists believe  that they were not connected politically. It is believed that they were the ancestors of the Native Americans found inhabiting the regions of the mounds by the first European explorers. Due to locality and tribal customs there is much variation in the shape, size, and purpose of mounds. Shapes include conical tumuli, elongated or wall-like mounds, pyramidal mounds, and effigy mounds (bird, animal, or serpentine forms).    (Paraphrased from nativeamericans.com, 2004)