In Ohio, a massive mound in the shape of a serpent snakes it's way across the landscape and no one knows who built or why. Thousands of miles away, a similar serpent mound of unknown origins slinks across the landscape of Loch Nell. Could there be a connection between the two sites? As Scott Wolter investigates, he discovers evidence that both sites were constructed using the same type of archaeoastronomy. Not only that, but a number of other animal shapes have been constructed as effigies across the Midwest. In a search for answers, he discovers there could be a connection between all the sites and one of America's biggest pre-Columbian mysteries--what led to the disappearance of the people of Cahokia, America's largest city in pre-Columbian times.