The Defenses of Prospect Bluff (Part 5)

The Defenses of Prospect Bluff (Part 5)
A surviving portion of the moat of the “Negro Fort” at Prospect Bluff on Florida’s Apalachicola River.

The fortifications and cannon of Prospect Bluff offered a daunting challenge for would-be attackers. These defenses were extensive and strong.

It was quiet in mid-July 1816 as U.S. Navy gunboats waited in Apalachicola Bay for the arrival of American troops.

This post is part of a series marking the 200th anniversary of the U.S. campaign against the Fort at Prospect Bluff (or “Negro Fort”). Read previous posts in this series at the bottom of the page.

Despite the great significance of the fort, which has been designated as the British Post National Historical Landmark, very little is really known of its appearance and design. This has been changing over the last few months thanks to the efforts of the U.S. Forest Service and the National Park Service.

The faint outline of the fort can be seen on this modern LIDAR (laser radar) image. Courtesy Northwest Florida Water Management District

The massive fort was designed by the British during the fall of 1814 and featured multiple layers of defensive works. Work by the U.S. Forest Service to clear more of the site has exposed unexpected features and revealed a remarkable state of preservation in some of the outer works.

It is also expected that a week-long archaeology workshop recently conducted at the site by the National Park Service will reveal a tremendous amount of new information about the interior design of the fort. The largest team of archaeologists ever to work on the site spent time examining its archaeology with a remarkable array of new technology. The results are still being analyzed and will be presented in a future report. Some of the finds have been startling.

To examine the design in a less confusing way, I will use diagrams and photos to enhance this discussion.

Outer Entrenchment

The outer entrenchment of the fort based on archaeological remains and an 1818 map prepared by the U.S. Army.

The outer perimeter of the British Post was protected by an extensive rectangular entrenchment and breastwork. Eyewitness accounts indicate that this defensive line was constructed during the winter of 1814-1815 by British Royal and Colonial Marines, Red Stick Creek and Seminole Indian warriors, a force of Spanish soldiers forcibly removed from Pensacola by the British and a battalion of regular British infantrymen.

The size and location of the outer entrenchment is best known from a plan of the fort prepared in 1818 by Major James Gadsden of the U.S. Army. His plat was drawn after the construction of Fort Gadsden on part of the site of the British Post by U.S. troops and, unfortunately, omits the location of structures such as barracks, etc.

A number of critical parts of the design of the outer entrenchment can be seen on Gadsden’s map. It shows that the sally port or gate of the fort was at about the midpoint of its northern side and was protected by an additional breastwork that extended north beyond the main line of the entrenchment.

Analysis of lidar (laser radar) data for the site 2015-2016 showed that much of the outer entrenchment was intact but lost in heavy growth. Archaeologists Andrea Repp and Rhonda Kimbrough from the U.S. Forest Service hacked through dense vegetation and found that sections of the breastworks and trench did still exist. Crews have subsequently cleared sections of the outer entrenchment to reveal remarkably well preserved fortifications from the War of 1812.

The northeast and northwest corners of the outer entrenchment were protected by bastions of stronger construction. The same was true of the northwest and southwest end of the breastworks except that less enclosed demi-bastions were used to add extra strength to the outer lines at those points.

Lidar (or laser radar) revealed once again that the bastions were intact but covered by a dense growth of palmetto and other vegetation. U.S. Forest Service archaeologists located these intact structures and have since directed crews in the clearing of some sections. This work has revealed that the eastern full bastions and southern demi-bastion survive in a remarkable state of preservation.

The interior palisades have been added to the map of the outer entrenchments. They are represented by the dotted line in the center.

Interior Palisades

A second line of defense was was offered by a roughly triangular inner palisade that ran from the center or citadel of the fort out to the edge of the bluff.

No trace of this stockade is visible at the site today nor does its line show on radar, but its approximate design and location can be recreated using the 1818 Gadsden sketch of the fort. It was built of stout logs, one of which was uncovered by U.S. Forest Service archaeologists ahead of the construction of a new boardwalk at the site.

The purpose of this wall was defensive, but it also appears to have separated the areas of the fort occupied by the British military in 1814-1815 from areas occupied by civilians. Although most of their exact locations are not known, the barracks and other military structures of the fort stood within the palisade.

An interesting discovery was made along this line in February 2016. The photograph below was taken at the moment when a small mound of earth was found in an unexpected part of the fort. This mound had been obscured by undergrowth since the site was developed as a park in the 1960s and was only noticed because winter weather had reduced the growth just enough for it to be spotted as researchers were trying to follow the trace of the outer entrenchments.

Archaeologists examine the “mound” of one of the original field ovens of the fort.

Credit for identifying its probable use is due to Mark E. Hubbs, an archaeologist for the U.S. Army Space and Missile Defense Command (yes, they have archaeologists!) on historic Redstone Arsenal in Huntsville, Alabama. Hubbs takes part in War of 1812 living history events and recognized the similarity of the mound to extremely rare British field ovens of that era.

Hubbs visited Prospect Bluff during a week-long field school conducted by the National Park Service and helped identify two more possible field ovens. All three appear to have been located within the lines of the inner stockade. A fourth such feature has been located at the site of Nicolls’ Outpost, an advanced base established by the British at what is now Chattahoochee, Florida.

British field ovens of the early 19th century were constructed completely of earth and each one could bake or warm enough food to feed a surprisingly large number of men. If future research verifies the identity of the four features found at British fort sites on the Apalachicola River, they will represent the largest known grouping of surviving War of 1812 British field ovens in the world.

The water battery is the angular redan or triangle-shaped structure facing the river at the bottom of the map.

Water Battery

Several of the fort’s heaviest guns were placed in a water battery at the edge of the bluff. This triangular earthwork or redan was designed to allow cannon to fire up and down the river on an enemy approaching by water. Strongly built, this part of the fort was later incorporated into the design of Fort Gadsden when it was constructed by U.S. troops in 1818.

Some modern authors have described Prospect Bluff as a towering eminence but its top elevation is actually only about 16-feet above sea level. This does not sound very imposing until it is realized that the river banks between the fort and Apalachicola Bay are rarely more than 1 to 5 feet above sea level.

Prospect Bluff was the southernmost elevated spot not subject to annual flooding by the Apalachicola River. The placement of the water battery on a slight projection of the bluff line provided its cannon with an excellent fields of fire.

The elevation and placement of the cannon would allow them to direct particularly destructive fire at approaching boats or ships. The height of the bluff was low enough for the gunners to send solid shot “skipping” across the surface of the water, much as it is possible to skip a stone across the water of a pond. This technique made it possible for the artillery of the early 19th century to strike enemy ships at or near the waterline.

The Apalachicola River as seen from the British Water Battery.

Another feature of the water battery is evident from the 1818 plat of Fort Gadsden. The cannon were placed so as to fire through embrasures or openings in the earthwork walls instead of over the top of the ramparts. It is not known if this was a feature of the original British Post or if changes were made during the conversion of the site by American troops.

If the design of the battery allowed the fort’s heavy cannon to fire through embrasures in 1816, then it would have been possible for Garcon’s gunners to fire and reload without exposing themselves to enemy fire.

Another representation of the battery is found on a sketch of Fort Gadsden prepared by an officer during the time it was occupied by the U.S. Army. It shows that the exterior of the walls were reinforced by squared logs or planking that helped prevent the earthworks from eroding into the river during times of high water or rain.

As is the case with the embrasures, it is unclear whether this was part of the original British design or if American troops added to the battery during their building of Fort Gadsden on the site.

The water battery can still be seen today.

The interior moat has been added to the map and is represented by the blue shape in the center of the fort.

Interior Moat

A wet moat surrounded the interior citadel or magazine of the fort. Its location can be seen on the diagram at right.

As the diagram shows, the moat fit into the circular tip of the rough triangle formed by the lines of the inner palisade. It was located near the center of the fort complex.

Water to fill the moat flowed in from two ditches. One can be seen on the diagram leading from the point of the southeast bastion in the outer entrenchments. The other ran in a straight line to the ditch on the south side of the outer entrenchments.

The design of the moat as shown here was taken from James Gadsden’s 1818 plat of the fort, although lidar images and ground inspection verify the basics of his sketch.

The moat would have presented a significant problem for any attacking force of infantry. Should enemy troops make it past the outer entrenchments, they would still have to breach the inner palisade in order to reach the moat itself. It was deep and wide enough to make crossing it a formidable task.

One of the projections or “rabbit ears” of the inner moat still holds water during rainy weather.

The inner moat is one of the better preserved parts of the original British Post or “Negro Fort.” It can be seen with little difficulty and during times of wet weather still holds water as it was originally intended to do. The northern side is now somewhat obscured, probably due to the effects of the explosion that destroyed the Fort at Prospect Bluff in July 1816. The rest of its line, however, remains quite clear.

While the moat is largely octagonal in design, attention is immediately drawn to the odd projections that extend from its western side. Often described as “rabbit ears,” these projections are well-preserved and hold water during times of rain. Their function is unknown and recent research has deepened the mystery.

Survey of the moat area using ground penetrating radar (GPR) was conducted this spring by archaeologists participating in a workshop hosted by the National Park Service. While the data from that work is still being analyzed, NPS archaeologist Michael Seibert reports that it has revealed the possibility of another, now obscured, “rabbit ear” projection on the north side of the moat (left in the diagram).

An inspection of the heavily overgrown southern side of the moat also indicates that there might be another such projection or “rabbit ear” there.

One possibility raised in recent months is that the “rabbit ear” projections might actually be the arms of a six-pointed star. Could the inhabitants of Prospect Bluff have been working to further strengthen the fort by building a star-shaped earthwork and moat around the central citadel?

Star forts were common features of British military construction during the American Revolution and War of 1812. A well-preserved one can still be seen at Ninety-Six National Historic Site in South Carolina. American military engineers also employed star-shaped designs during this era. The base of the Statue of Liberty stands on a star fort built by the U.S. Army to defend New York City.

If the African-American inhabitants were strengthening their citadel by surrounding it with a star fort, such work would explain enigmatic eyewitness accounts from 1815-1816 that mention “improvements” being made to the post. Further research will be required to either verify or discount this theory.

The citadel is the octagonal structure shown in this 1818 drawing by engineer James Gadsden. Courtesy National Archives

The Citadel or “Magazine”

The real power of the fort – and tragically its greatest weakness – was its central stronghold or citadel. Much like the keep of a Medieval castle, this octagonal structure represented a final but formidable defensive point for the fort.

Often called the “magazine” because it was the scene of the explosion that destroyed the Fort at Prospect Bluff in July 1816, the octagonal citadel was actually a strong fortification. Gunpowder was stored there, but it also functioned as a storehouse for arms, uniforms, equipment, provisions and other necessities. British accounts suggest that officers’ quarters and other tfacilities were located in this structure.

Eyewitness descriptions of the fort indicate that this octagonal structure had earthen ramparts 18-feet thick and 15-feet high. Archaeology at the site shows that its walls were made of round logs and that the angles of the octagon were formed by mortised joints. Cannon were mounted on top of the structure, which engineer James Gadsden considered the “Negro Fort” proper, as is indicated by the notation he placed in its center.

The main octagonal structure was surrounded by two palisade walls and the inner moat. One of the palisades ran around the structure on the inside of the moat, while the second was the somewhat circular eastern angle or “point” of the inner palisade (refer to the diagrams above).

An anomaly in the line of the palisade inside the moat may reflect the location of the gate or sally port leading into the citadel. This can be seen at the upper right of Gadsden’s sketch of the citadel (see above). A freehand map of the fort drawn by a Spanish surveyor in 1815 also shows an anomaly at this point of the octagon.

The primary magazine of the fort contained around 300 barrels of powder and was located on the north side of the citadel (left in the Gadsden sketch above). The door to the magazine opened into the interior of the citadel. Unfortunately, this door faced south – the direction from which enemy ships were most likely to approach.

The fort as it appeared in July 1816.


The size and strength of the fortifications at Prospect Bluff were impressive, but even more remarkable was the collection of artillery that lined the walls.

An inventory of the military supplies in the fort was taken following its capture and provides an accurate list of its cannon. The list is actually larger than generally stated by modern writers:

One 32-pounder

Three 24-pounders

Two 9-pounders

Three 6-pounders

One 4-pounder swivel

One 2-pounder swivel

One 5 1/2-inch howitzer

These twelve guns represented one of the most powerful collections of modern artillery in Florida at the time of the 1816 campaign. The 32-pounder and three 24-pounders were most likely mounted in the water battery, while the other guns were placed throughout the fort and on top of the citadel.

Also in the fort at the time of the 1816 attack were an estimated 467 barrels of gunpowder, more than 500 boxed British muskets, swords, uniforms, bayonets, cartridge boxes and more than 23,000 gun flints.

Hopefully his article helps your visualize the fort as it appeared on July 14, 1816. The first action of the campaign would take pace the next day and I will post on that tomorrow.

To read previous posts in this series, please follow the links below:

July 10, 1816: Prospect Bluff Campaign began 200 years ago today

July 11, 1816: The Fort at Prospect Bluff

July 12, 1816: Gunboats No. 149 and No. 154 at Apalachicola Bay

July 13, 1816: The Year Without A Summer

Please click this link to continue to the next article:

July 15, 1816: Garcon challenges the U.S. Navy