ST. AUGUSTINE, Fla. -- A dull BOOM! startles guests checking into a waterfront motel near St. Augustine's historic district. The desk clerk doesn't even look up.
People here are accustomed to the firing of cannons atop the Castillo de San Marcos, one of three forts that draw visitors to the nation's oldest city.
The diamond-shaped fort stands at the edge of Matanzas Bay, with a commanding view of -- and firing position on -- ships approaching St. Augustine.
Construction of the Castillo began in 1672, ending for the first time in 1697. Additions and renovations have been done over the centuries by the fort's Spanish, English and American masters.
The fort's 33-foot gray walls are constructed of coquina. The soft shellstone, quarried on nearby Anastasia Island, "swallowed" cannonballs, rather than cracking under their impact.
Outside are the moat and some remains of a log defense, the Cubo line. Rather than alligator-filled water, the moat contained vicious Spanish bayonet cactus.
Inside are vaulted-ceiling chambers used in the mid-1800s as prison cells for Indians such as Osceola, who was captured under a white flag of truce.
Originally, though, the mostly windowless rooms were used to store a year's supply of necessities, such as rice, flour, beans and coffee for the town. Spanish soldiers worked at the Castillo -- in 24- to 48-hour shifts -- but no one lived there.
"This was a giant fortified warehouse," says National Park Service ranger Joe Mills.
That changed in 1702, during the War of Jenkins' Ear: a conflict that erupted from Britain's outrage over Spain's alleged mistreatment of its merchant sailors, notably the cutting off of Capt. Robert Jenkins' ear.
Thirteen hundred townspeople crowded into the Castillo with the 200 soldiers. For 50 days they huddled in the mud and dirt of the interior courtyard, waiting for the besieging British to go away.
But they did have one comfort. On the south side of the fort are what park rangers say may be the first flush toilets in the New World -- a couple of latrines washed out twice daily by the tide, known as las necesarias.
Up on the fort's broad gundeck are about 30 cannons and mortars. Some are original; others were captured in U.S. wars or loaned from private collections.
Some have names, such as El Camilo: A small plaque says it was "named for a Roman boy employed in non-Christian rituals."
Some of the cannons are fired during re-enactments of different historical periods held regularly at the castle. Area residents and visitors in period dress portray soldiers and townsfolk.
Re-enactors also fire cannons at Fort Matanzas, about 14 miles south. This fort, built of coquina as well, is so much smaller that four of it would fit into the Castillo's courtyard without touching. But it was a vital early-warning and defense post on the southern water approach.
The name Matanzas derives from the fate of hundreds of French soldiers led by Jean Ribault who were swept south in a 1565 hurricane while going to attack St. Augustine. They were caught by Spanish forces led by the city's founder, Gen. Pedro Menendez de Aviles, who ordered them slain 10 at a time.
Matanzas is Spanish for slaughters.
Visitors reach the little fort on Rattlesnake Island via a free ferry running once an hour. Rangers conduct tours of the tower, and visitors can climb to the observation deck, see the officers' and soldiers' quarters, and check out the powder magazine.
Built between 1740 and 1742, Fort Matanzas became a U.S. possession in 1821. But it deteriorated into a cracked ruin and sprouted trees. Restoration didn't begin until after it and the Castillo were named national monuments in 1924.
The Fort Matanzas grounds also feature nature trails, including a handicapped-accessible boardwalk, as well as places to fish, picnic and hike.
Just outside the city gates of St. Augustine, a plain metal gate at the end of a dead-end street marks the entrance to the state-owned site of Fort Mose (moh-ZAY), the first legally sanctioned settlement of black people in what became the United States.
In the early 1700s, British slaves in the Carolina territory learned that the lives of their counterparts in Spanish Florida was better. Spanish slaves could sue over ill treatment, work independently and make money to buy themselves free.
Word quickly spread among slaves in Carolina of a 1733 Spanish decree, which stated that anyone who reached St. Augustine, accepted Roman Catholicism and swore fealty to the king of Spain would be granted freedom. By 1738, so many had risked everything to reach St. Augustine that Gov. Manuel de Montiano decided they should have their own town.
About two miles north of the Castillo, the ex-slaves built a wooden fort and a town, Gracia Real de Santa Teresa de Mose. A priest was assigned to live with them, teaching them the ways of the church as well as how to read. That was forbidden to English slaves.
Fort Mose was St. Augustine's northern lookout. In 1740, the Mose militia lost its first engagement with forces led by Gen. George Oglethorpe, and the fort was heavily damaged. But two days later, the militia, along with some Spanish and Indian support, retook the site, leading the British to dub it "Bloody Moosa."
Today, the area is peaceful. No trace of the fort is visible. Most of the activity is that of fiddler crabs skittering away from visitors splashing through the marsh grass toward an island where archaeologists have dug for clues about life at Mose.
"You really have to use your imagination out here," says ranger Steve Gard, picking up litter left behind by people who go to the island to fish.
State officials are working on a plan to build a historical center at the site. It will house a traveling exhibit about Fort Mose put together by some members of the archaeological team that worked on the island.
For now, there are Fort Mose re-enactments as well. Mr. Gard portrays a slave-catcher, and a local teacher plays a runaway slave. Students from the local junior ROTC train as militia members and get to fire old-style guns.
"They love it," says Mr. Gard.