The mysterious tribal people known as The Calusa ruled the area between Tampa Bay and Fort Myers for centuries, with their kingdom having existed at least as early as 1150 BC and vestiges of it surviving as late as the 18th century. Mound Key off the coast of Fort Myers, is believed to have been the original site of the Calusa kingdom's capital city of Calos.
Strange as it may sound, Mound Key is actually a mostly artificial island, created from the Calusa tribe's garbage (oyster shells, fish heads, animal bones, broken and discarded pottery) over the course of centuries. Some have noted that the placement of the waste materials seems deliberate, as if the whole thing was treated like an art project of sorts, with what has been described as "mounds, water courts, and canals".
Once the Spanish arrived, it was all over for the Calusa. In 1566, a bunch of Spaniards showed up and soon built a fort and settlement, and well, there went the neighborhood. A Jesuit mission was founded nearby, called San Antonio de Carlos, and they focused their efforts on converting the Calusa to Christianity. And as you can probably guess, that didn't go over too well. The Calusa had their own religion going on, which was rather complicated according to Wikipedia:
The Calusa believed that three supernatural people ruled the world, that people had three souls, and that souls migrated to animals after death. The most powerful ruler governed the physical world, the second most powerful ruled human governments, and the last helped in wars, choosing which side would win. The Calusa believed that the three souls were the pupil of a person's eye, his shadow, and his reflection. The soul in the eye's pupil stayed with the body after death, and the Calusa would consult with that soul at the graveside. The other two souls left the body after death and entered into an animal.
Calusa ceremonies included processions of priests and singing women. The priests wore carved masks, which were at other times hung on the walls inside a temple. Hernando de Escalante Fontaneda, an early chronicler of the Calusa, described "sorcerers in the shape of the devil, with some horns on their heads," who ran through the town yelling like animals for four months at a time.
The Spanish eventually left and gave up trying to convert the natives, but the damage had been done - they'd brought diseases with them for which the Calusa had no natural immunity. The last of the Calusa had vanished by 1750, and for the subsequent century Mound Key was used by pirates, American pioneers (even Daniel Boone and his brother Squire made their way to the Sunshine State at one point) and fishermen (Cuban, Portuguese, Spanish, etc.)
Then in 1894, the followers of a scientific/religious belief system known as Koreshanity arrived in the area. They built a community based on their utopian "Hollow Earth" ideas, during which time they acquired most of the property on Mound Key. In 1908, after the death of their leader, Cyrus "Koresh" Teed, their numbers went into decline. Teed was buried on nearby Estero Island and posthumously became the subject of another controversy when stories began to circulate that anyone approaching or touching his tomb met with bad luck, death, or insanity. Teed's tomb, along with his body, was swept away in a hurricane in 1910.
In 1961, the few remaining Koreshans decided to give up and donate the island, as well as other land in the nearby town of Estero, to the state of Florida. It was used to form a park, which is administered by the Koreshan State Historic Site. Because of this, the Koreshan sect are more famous today than ever - and yet few have ever heard of the Calusa civilization, who created the island in the first place.
Readers of my Unusual Kentucky blog may recall that Cyrus Teed and his Koreshans turn up in the strange case of the wandering occultist-opportunist Editha Salomon, aka Anna Sprengel, aka Ann O'Delia Dis Debar, Laura Horos, Ellora, Madame Helana, Swami Viva Ananda, Della Ann O'Sullivan, Angel Anna, Claudia D'Arvie, Editha Gilbert Montez, Vera Ava, Blanche Solomons, etc.