Fort San Antón de Carlos

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Fort San Antón de Carlos (1566-1569) - A Spanish Colonial era Fort established in 1566 on Mound Key, Lee County, Florida. Named Fort San Antón de Carlos for the Catholic patron saint of lost things. Abandoned in 1569.


Fort San Antón de Carlos was established in 1566 on the order of Pedro Menéndez de Avilés. In February of 1566, Menéndez arrived off the southwest Florida Gulf Coast with 500 men in seven vessels here he met with King Caalus of the local Calusa tribe on what is known today as Mound Key. The Key was home to the Calusa people and the town of Carlos or Caalus was the capital of the Calusa Kingdom.

The Key (a low-lying island) featured two large shell-midden mounds one of which held the king's house, reputed to hold some 2000 people and the other (larger) mound that housed the town and later the fort. A central canal bisected the key and ran north-south between the two mounds. At the north end of the key were several smaller burial mounds and a "water court", an enclosed body of water used to hold live fish.

Agreement to build the fort and a mission was obtained and on 15 Oct 1566, the order to start fort construction was given and Captain Francisco de Reinoso and his 30 men began the task. From archeological evidence, it appears that the fort was constructed on the second shell-midden and that it was large enough to contain some 36 structures. It also appears that a unique style of “tabby” construction was used, using shell materials from the midden for the fort wall foundation. The Spanish also used the tabby as mortar to stabilize the wood posts in the walls of their wooden buildings. This was the only Spanish fort known to be built on a shell mound.

By 1569 tribes all along the Florida coast had turned against the Spanish and they were forced to abandon and destroy Fort San Antón de Carlos.

Current Status

The Fort San Antón de Carlos archaeological site (8LL2) is located within the Mound Key Archaeological State Park which encompasses most of Mound Key. There are no visible remains of the fort. The Key is located in Estero Bay and access by visitors is typically by a private boat launched from Koreshan State Park or Lovers Key State Park. There are boat landing sites on the northwest and southeast sides of the island and a 3/4 mile trail that crosses the island connecting both of the boat landings and both of the mounds. The landing on the northwest side of the island is most suitable for powered watercraft. The landing on the southeast side of the island is most suitable for canoes and kayaks. There are no facilities on the key. There are some interpretive displays along the trail. Mound Key is managed by Koreshan State Park, in Estero.

Location: Mound Key, Lee County, Florida.

Maps & Images

Lat: 26.42247 Long: -81.86400

GPS Locations:

See Also:


  • Thompson, Thompson, Marquardt, Walker, and Newsom, Discovering San Antón de Carlos: The Sixteenth-Century Spanish Buildings and Fortifications of Mound Key, Capital of the Calusa, Historical Archaeology (2020) 54:334–353, Pdf.


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