Built during the Late Woodland period by mound builders, Effigy Mounds became a regional and cultural phenomenon spanning Iowa, Minnesota, and the Southern Wisconsin-Northern Illinois Border. There are mounds with geometric shapes, and over 200 common animal themes. An amazing feat, considering the prehistoric tools used by the Native Americans at the time.
What separates these mounds from others like it is the fact that these lack traded goods from long-distance tribes, or any sort of valuables. Some burial mounds only possess a simple cooking pot. This practice of burying their people in humble means may suggest that the communities that these mounds originated from were egalitarian, believing that all people were equal within the communities and even politically. But the practice of many that lack any markings that are geometric in shape still remain a mystery.
Today, only a handful remain intact due to agricultural development. That, however, has not stopped the theories of why they were built. Archaeologists believe that the geometrically shaped mounds were meant as a place of burial or sacred ceremonial sites, such as funerals, because some mounds had items believed to be used during a burial. Items that could have been used in the afterlife to make their transitions easier and more comfortable.
Native Americans have argued that they were sites of refuge, not of burial. That these were places of great religious importance, such as a place for birthing children. It could be suggested, that since some of these mounds lack any burial items, that this may have been a place of worship or clan meetings.
Others have suggested that they were built in observance of celestial bodies. There is a theory that the placement and shape of the mounds is what the Native American tribes of the day believed how the universe was shaped.
Some archaeologists suggest that the animal-shaped effigy mounds were territorial markers. Since this was a race of hunter-gatherers, it could be that they marked where one group, or tribe, had positioned for themselves to gather crops or hunt for their meat. It is also thought that each clan had an animal spirit, or an animal representative, and the mounds were built to honor those spirits.
Without the mound builders present, and only mythology and stories handed down through generations one could only guess why they were originally built. As scientific data has proven inconclusive, much of the theories presented can only be speculation of a race long past.