Fort Matanzas was built by the Spanish in 1742 to guard the southern mouth of the Matanzas River, called Matanzas Inlet, which could be used as a rear entrance to the city of St. Augustine. Such an approach avoided the primary defense system in St. Augustine which was centered at Castillo de San Marcos.

The fort, known to the Spanish as Torre de Matanzas (Matanzas Tower), is a masonry structure made of coquina, a common shellstone building material in the area. The marshy terrain was stabilized by a foundation of pine pilings to accommodate a building 50 feet long on each side with a 30 foot high tower.

The standard garrison of the fort was one officer in charge, four infantrymen, and two gunners, though more troops could be stationed if necessary. All soldiers at Fort Matanzas served on rotation from their regular duty in St. Augustine.

Five cannon were placed at the fort—four six-pounders and one eighteen-pounder. All guns could reach the inlet, which at the time was less than half a mile away.

Fort Matanzas National Monument was designated a United States National Monument on October 15, 1924. The monument consists of a 1740s Spanish fort called Fort Matanzas, and about 100 acres of salt marsh and barrier islands along the Matanzas River on the northern Atlantic coast of Florida.

It is operated by the National Park Service in conjunction with the Castillo de San Marcos National Monument in the city of St. Augustine.

The word Matanzas is Spanish for slaughters and this fort came to be called this because this is where Admiral Pedro Menendez de Aviles marched fourteen miles south of his Spanish post with fifty soldiers to find the French shipwrecked at a river inlet and there massacred nearly 250 of the shipwrecked French Huguenots, including their leader Jean Ribault.

Only three Spanish soldiers were in residence at Fort Matanzas when the United States took possession in 1821.

Upon Leaving Castillo De San Marcos, I drive south on state route 1A1, to Fort Matanzas National Monument which by extension is a fort protecting the back water route to the main fort in San Augustine. Fort Matanzas provides free parking and a free ferry ride to the fort located on Rattlesnake island a short distance across the Matanzas River.

This park has become one of my favorites forts, not only because it has free access but because the structure is all original, even thought it had to be almost completely rebuilt by the park service. Now, it is standing on it′s own without requiring any external supports and has replicated furniture and artifacts of the period.