Several pre-Columbian cultures in North America were collectively termed "Mound Builders", due to the characteristic mound earthworks which indigenous peoples erected for an extended period of more than 5,000 years. The "Mound Builder" cultures span the period of roughly 3500 BCE (the construction of Watson Brake) to the 16th century CE. These burial and ceremonial structures were typically flat-topped pyramids or platform mounds, flat-topped or rounded cones, elongated ridges, and sometimes a variety of other forms. They were generally built as part of complex villages.

Source: Wikipedia