Mound Key is located in Southwest Florida in the Estero Bay. It is a 125 acre site and was the military center and ceremonial center for the Calusa Indians. The island's foundation is made of marl (a clay-like material) which was packed down and combined with shells and rocks to raise the level of the ground. They then used shells from the sea bottom, driven spiral down into the muddy surface of the mound.
They also made large embankments and moats to protect their settlement there, which are suprisingly large considering they didn't have big tools or domestic animals to help build it. There were anywhere from 30-50 settlements that the Calusas made, but Mound Key was the biggest. The remnants of their settlement are still there, and Mount Key is open to tourists almost all year round.