When the people that became known as the Mound Builders first arrived in Ohio, they already had their religious beliefs firmly entrenched in their daily lives. Where they came from is not completely certain. We do know that archeological evidence indicates they migrated up the Mississippi River and then spread out through it's tributaries.
In the early 19th Century a singular conical mound was excavated. This mound happened to be located on the farm of Thomas Worthington, one of Ohio's early governors. It is located just west of Chillicothe. Although his estate was originally named Mount Prospect Hill, he changed the name in 1811 to Adena after he came across that name while reading an ancient history book. That excavated mound became known as the Adena Mound. Over time more burial mounds were studied and it became apparent that those who built the burial mound on Thomas Worthington's property also built many 1000 more mounds across the state and that these mounds were the first mounds built in Ohio.
The Adena Culture was widespread throughout the state. Many of these singular burial mounds can still be seen. Some tools and recovered pottery remnants suggest they had developed some farming skills to supplement hunting skills. It is believed that the late Adena Culture was most likely responsible for constructing the Great Serpent Mound in southern Ohio.
The first mounds studied were found on land owned by W.C. Clark in the 1820s and was known as Clark's Works. However, towards the end of the 19th Century Ohio Historians and Archeologists wanted to make a definitive presentation at the 1892 World Columbian Exposition in Chicago. To illustrate this exhibit, it was decided an extensive study be made of one of Ohio's major earthworks. Clark's Works was selected. However, at the time of this study, the land had changed hands and was then owned by Mordecai Cloud Hopewell. Hence, the name Hopewell was given to this cultural group.
The Hopewell Culture was more robust in their mound building than the older Adena Culture. They continued in part building burial mounds, but they also began expanding their constructions by building massive earthwork complexes. There seems to have been some common design elements used in these earthworks which was primarily a very large circular structure attached to an even larger rectangular embankment. These massive embankments were not used for burial purposes although there were often burial mounds inside the enclosures as well as outside the walls.
Within the burial mounds there was increasingly more and more artifacts placed alongside the honored leader. These artifacts included pottery, carvings that displayed increasingly complex forms and craftsmanship. The Hopewell Culture also expanded the farming practices the Adena Culture had begun to develop. This allowed for larger communities not dependent solely on hunting. A type of maize was also beginning to be found in some sites, but it was not widespread. Sunflower and natural grasses were being cultivated.
The remains of multiple large earthworks were common in some areas separated by just a mile or so. There was also evidence to suggest that the Hopewell Culture carried on extensive trading with other people across North America.
Sometime around 1000 AD we begin to see another dramatic shift in the Mound Builders. They stop building their typical circular / square enclosures and start constructing what appears to be irregular walled perimeters on high plateaus overlooking navigable waterways. Mortuary practices have mostly disappeared compared to the Hopewell, but there were some small burial mounds found inside the perimeter walls. Those sites where exhumations have been conducted indicate that the elaborate burial rituals were mostly gone as were the inclusion of artifacts that were once included with honored dead.
This period lasted a few hundred years or so and became known as the Fort Ancient Culture. The Fort Ancient Culture was primarily located in southern Ohio. The first of these structures was identified as Fort Ancient. Since then a number of these irregular structures have been discovered. This was the last of the Mound Building Cultures.