It is an amazing stone fortress in a star shape that guarded the eastern coast of florida and the city of St. Augustine. It was in a very important location to guard trade along the coast and with Europe.

It is in absolutely pristine condition and managed by the National Park Service. It is open to the public and it is a great window into the past.

This is part of my journey around Medieval America

This is a model of the castillo. It shows the star shape of the fortress.

The big thing about this fortress was cannons both in firing them and in defense against them. And it is quite unique among all the fortresses in the world in that it is cannon ball proof! Yes, cannonball proof. This is because of the unusual material it is made from: Coquina.

Coquina is a stone locally sourced in Florida and it is sedimentary rock formed from the shells of mollusks.

And it is quite remarkable as the walls of a fortress because it is immune to cannonball fire. This complex conglomeration of shells simply crunches under cannon fire. It compresses and absorbs the impact. So, the walls don't crumble they just absorb the blow. It's quite amazing.

And it has proven to be true. In 1740 the British bombarded the fortress for 27 days with cannons and the fortress held strong.

They have preserved the whole castle in its original state as a fortress on the water in the 17th and 18th centuries so you can get an amazing glimpse as to how it was.

Watch this short clip showing the fortress.

The History of Castillo de San Marcos