Why Coquina?

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Since it was founded in the age of heavy cannon usage, and because brick-clay is harder to come by in the sandy soils of Florida, a substitute was needed. Because it is native to Florida, the sedimentary Coquina rock was the obvious choice for the construction of San Marcos. Although, when first mined, it is far too soft to be used for building purposes, Coquina may be left to dry in the hot Florida sun for periods up to two years, hardening it sufficiently. The final product is resistant to cannonfire because when the iron balls strike the hunks of Coquina that compose the fortification's walls, the shell fragments compress instead of propagating cracks like the stone walls of old castles native to Europe. At the time, across the pond, castles were being built primarily out of brick, because it was softer than solid rock and thus could absorb the force of cannonfire without shattering.