The limestone fortress built from shells and sand

Countries & Cities · Published 15 October 2026 Swipe more like this →

In short: St. Augustine’s Castillo de San Marcos is a marvel of early military engineering. Rather than standard stone, it was constructed using coquina—a unique limestone formed from sand and mollusk shells. This material choice defined the defense of Florida’s oldest city and remains a centerpiece of the region's historic coast.

The Castillo de San Marcos, located in St. Augustine, began construction in 1672. It stands as a primary landmark of Florida’s Historic Coast, a region defined by its rich colonial and civil war history. The fortress is notable for its construction material: blocks of coquina rock. This specific type of limestone is composed of sand and mollusk shells, sourced from local coquina quarries such as those found in Anastasia State Park. The city of St. Augustine is recognized as the oldest in the nation. Its vibrant arts district on Aviles Street has flourished since the 1930s. Visitors can also explore history related to native people and the American Civil War.

The geography of St. Johns County provides a diverse tapestry of water-related habitats. The Guana River Marsh Aquatic Preserve sits within the Guana Tolomato Matanzas National Estuarine Research Reserve. This area features a complex mix of environments, including barrier islands, salt marshes, and lagoons where freshwater meets brackish water. These habitats serve as critical refuges for endangered wood storks, sea turtles, and various shorebirds. The preserve is uniquely situated within a national estuarine research reserve. It provides a haven for various shorebirds in addition to the endangered wood storks. These diverse environments are essential for the local ecology.

Beyond the historic center, the county offers extensive aquatic and upland recreation. Faver-Dykes State Park features tidal marshes and creeks, while the Pellicer Creek Aquatic Preserve provides a designated paddling trail. These waterways are integrated into the Great Florida Birding Trail, supporting a variety of local wildlife and offering residents and visitors a way to experience the region's diverse ecosystems through canoeing, kayaking, and birding. The Hiram Faver Trail provides a shaded path that ends at an overlook of Pellicer Flats. This area is characterized by longleaf pines and tidal marshes. The park also offers 1,600 acres of unspoiled beaches for hiking and geo-seeking.

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