The exploration and colonization of Florida by Europeans was a maritime undertaking. Because people, goods, and military power moved by ships at sea and on rivers, safe inlets and protected harbors were most important factors in deciding where to settle and what to defend. From a secure seaport, settlement could extend into the unknown and challenging interior, but constructing and maintaining adequate roads, and transporting goods by animals and carts was exceptionally difficult.
Its history of disrepair, destruction, abandonment, and reoccupation by various governments is typical of the remote forts in Florida that were as difficult to maintain as they were to defend.

Florida was under Spanish control, to varying degrees and with one twenty-year British exception, for more than three hundred years. From 1565 St. Augustine was the administrative center, situated on the "Highway of the Indies," now known as the Gulf Stream, that propelled sailing fleets containing the wealth of the New World back to Spanish ports. Here was the formidable Castillo de San Marcos, and the smaller forts Matanzas to the south and Mose to the north, that controlled entrance to the inlet, the harbor and the connecting rivers. The Castillo is the oldest masonry fort and the only 17th century fortification in the nation. On the Gulf Coast, Pensacola was the focus of Spanish settlement beginning with the failed attempt at settlement by Tristan de Luna in 1559. A series of Spanish forts guarded the entrance to Pensacola Bay including Fort San Carlos de Austria (1698-1719) and Fort San Carlos de Barrancas (1787-1814, rebuilt 1817)

On opposite banks of the St. Johns River, Fort San Francisco de Pupo and Fort Picolata, were constructed in the early 1700s to guard the river crossing of the Mission Trail and defended the River south of St. Augustine. Some missions also had their own fortifications, including at Mission San Luis de Apalachee in present-day Tallahassee. South of Tallahassee on the Gulf coast Fort San Marcos de Apalachee was established in 1679 to defend the St. Marks and Wakulla River entrances to the inland Apalachee region. Its history of disrepair, destruction, abandonment, and reoccupation by various governments is typical of the remote forts in Florida that were as difficult to maintain as they were to defend.