To oversee the Americas during the early sixteenth century, Spain created the "Laws of the Indies" in 1573, under which the town of "San Agustin" was established in 1598 (Waite). When pirates and Indians threatened the town, Spain's Queen Regent Mariana ordered the construction of a new fort made of stone, and so in 1672, construction on Castillo de San Marcos was begun and completed twenty-three years later in 1695 (Watie). .

             The fortress was constructed of 400,000 blocks of coquina shell rock that was quarried from Anastasia Island across the Matanzas River (Wiggins). Coquina, which means "little shell" is actually shellfish that died long ago and their shells have now become bonded together to from the stone (Castillo). Coquina was chosen was chosen for the fabric of the walls because it was easily shaped by the castle's artisans and did not succumb to cannon fire (Waite). But perhaps more importantly, it was a local stone that could easily be quarried and ferried across the bay to the construction site (Castillo). Stone masons, who were sent to St. Augustine from the Crown from Havana, Cuba, labored to produce the blocks for the construction (Castillo). The mortar to bond the blocks to one another was made on the construction site by baking oyster shells in kilns until they fell apart and turned into a fine white powder called lime, which was then mixed with sand and fresh water to produce the mortar that still holds the Castillo together today (Castillo). .

             The large-scale construction was undertaken by European-trained engineers and experienced "maestros de obras," masters of construction, trained in apprenticeships in Cuba (Waite). Author Elsbeth Gordon writes, "They worked stone into neat building blocks, steps, pilasters, and fluted columns with Doric and Ionic capitals" (Waite). .

             According to Gordon, workers erected "pier arches, half-round domes, stepped and curved gables, belfries, and neoclassic portals.