Horr's Island archaeological site

The Horr's Island archaeological site is a significant Archaic period archaeological site located on an island in Southwest Florida formerly known as Horr's Island. Horr's Island (now called Key Marco, not to be confused with the archaeological site Key Marco) is on the south side of Marco Island in Collier County, Florida. The site includes four mounds and a shell ring. It has one of the oldest known mound burials in the eastern United States, dating to about 3400 radiocarbon years Before Present (BP). One of the mounds has been dated to as early as 6700 BP. It was the largest known community in the southeastern United States to have been permanently occupied during the Archaic period (8000 BCE-1000 BCE).

The island is named for Capt. John Foley Horr, who raised pineapples on the island in the late 19th century. The Capt. John Foley Horr House was listed on the U.S. National Register of Historic Places on October 8, 1997. In the late 1980s, a development company planned to build a bridge to Horr's Island and develop it. In response to state law requiring an archaeological assessment of the island before it could be developed, the development company funded a research project. The research team carried out excavations for three months.

Four mounds were identified on Horr's Island, but Mounds B and C were found to be simple middens, and were not investigated in depth. A flexed burial was found in Mound B. The other two mounds were complex and appeared to be purposely constructed. Mound A, the largest at 20 feet in height, had a large pile of shells at its core. There was no evidence of prior habitation on the ground surface where the shells had been piled. Several layers of sand had been added over the shells. One layer of sand had charcoal added. The additions of sand by individual baskets could be distinguished by the variations in the amount of charcoal in the sand. The final layer of sand had shells mixed in it, and the mound was topped by another layer of shells.

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