Piling Grillage

Artist representation of the wooden post foundation beneath Fort Matanzas

NPS

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Historical/Interpretive Information/Exhibits

The marshy ground of Rattlesnake Island was less than ideal for a heavy stone fort, but brilliant construction techniques made it possible.

Techniques for building stable foundations in unstable environments have evolved and improved over time. In the 18th century, wooden foundations were often the best option in in places such as the marshy shores of Rattlesnake Island. Friction pile construction consists of sturdy pine poles sunk vertically deep into the marsh. The poles were then connected by a grillage of square timbers. The next step was to place the coquina stone on top of the grillage. A 1978 archaeological investigation of Fort Matanzas showed the wood foundation still exists. Over the years, this foundation has settled with the changing environment.