Mound Key: the Calusa Capital
October 2022 Newsletter
Archeologists and historians believe that at its height, the Calusa dominated much of southwest Florida from the coasts of modern Tampa Bay to the Thousand Islands and inland as far as Lake Okeechobee with as many as 20,000 Calusa in southwest Florida. Mound Key, an island in the center of Estero Bay between Estero Island and mainland Lee County, has been identified as Calus, the cultural capital of the Calusa.
Documents of Spanish explorations of the area have long indicated that this island was the Calusa capital. Since 2013, Florida and Georgia archeologists have been studying the island for physical evidence of the Calusa. What they’ve found confirms a manor that housed the Calusa leader and was large enough to contain gatherings of 2000 people.
The building was atop a midden as high as 32 feet above sea level. Middens are accumulations of shells, bones and dirt. By volume, it is estimated that the midden material could fill 200 Olympic swimming pools. This is about one-fifth of the volume required to build the Great Pyramid of Giza.
The excavations by the Florida Museum of Natural History and the University of Georgia were reported in the fall 2020 edition of American Archeology. The work included the creation of a detailed topographical map of the island and ground penetrating radar as well as excavations.
William Marquardt of the Florida Museum notes that “the architectural remains of the king’s house were easy to find but difficult to interpret at first. Detailed analysis and accelerated mass spectrometry dates led us to the realization that the structure went through at least three phases of building activity over several centuries, the earliest phase dating to around A.D. 1000.”
Part of the fascination with the Calusa is the group’s absence of agricultural activity. “For a long time, societies that relied on fishing, hunting and gathering were assumed to be less advanced,” adds Marquardt. “But our work over the past 35 years has shown the Calusa developed a politically complex society with sophisticated architecture, religion, a military, specialists, long-distance trade and social ranking – all without being farmers.” The Calusa’s diet centered around fish and shellfish. They used shells as tools, utensils, building materials, vessels for personal and ceremonial use and for adornment.
In addition to the mounds and the large manor, the Calusa dug canals and engineered fish corrals or watercourts. The enclosures, the largest of which measured 36,000 square feet or two-thirds of a football field, were built on a foundation of oyster shells surrounded by a three-foot berm of shell and sediment. It is thought that openings in the berms permitted the Calusa to drive fish into the enclosures where they were enclosed by nets or wooden doors and kept short-term until eaten, smoked or dried for later consumption. Fish bones and scales found in the watercourts are from schooling fish like mullet, pinfish and herring. Radiocarbon dating places the building of the watercourts between 1300 and 1400 A.D.
Spanish ships arrived on the coast of southwest Florida in the early 16th century and according to their records, they began building Fort San Anton de Carlos in 1566 to serve as a Catholic mission. The Spanish had little success in converting the Calusa and the fort was abandoned after only 3 years in 1569.
The fort is the earliest known North American example of “tabby” architecture. Tabby is a rough form of shell concrete made by burning shells to create lime which is then mixed with sand, ash, water and broken shells. At Mound Key, tabby was used as mortar to stabilize the wooden posts of the fort. The archeological team has unearthed walls of the fort, ceramic shards and beads suggesting that additional work needs to be done.
“Seeing the straight walls of the fort emerge, just inches below the surface, was quite exciting to us,” Marquardt said. “Not only was this a conformation of the location of the fort, but it shows the promise of Mound Key to shed light on a time in Florida’s history that is very poorly known.”
This article is based on information from the Florida Museum website and the Smithsonian Magazine.
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