[5][6] The lighthouse has an iron-pile foundation with a platform, and a skeletal, octagonal, pyramidal tower, which is painted red.
The United States Lighthouse Board reported that "Carysfort Reef picks up twenty percent of all the wrecks between Cape Florida and the Tortugas, a space of 200 miles (320 km).
"[7] A survey of the Florida Keys in 1823 to locate sites for potential lighthouses and other aids to navigation produced a recommendation that a "floating light", or lightship, be placed on Carysfort Reef.
Congress appropriated funds for the lightship in 1824, and a 220-ton schooner named Caesar was built in New York and launched in 1825.
The shipbuilder's agent bought the ship back for US$10,000, but it took a year to repair and refit it, and find a crew.
The Caesar, under the command of lightship keeper John Whalton, reached its station and first lit its two lanterns in April 1826.
Whalton's wife and children, who lived in Key West, would visit the lightship for a few days at a time.
In September 1835, the Florida was severely damaged in a hurricane, with the lanterns broken, but the ship was repaired.
Whalton and one helper were killed, and two of the other three were wounded, but the three survivors managed to escape back to the ship, where the rest of the seven man crew awaited, along with Capt.
Some captains thought that the lights on the lightship were deliberately dimmed or extinguished in collusion with wreckers.
The site was under 4.5 feet (1.4 m) of water, and the reef was not solid, as expected, but consisted of a hard shell over calcareous sand.
[12][13] Construction of the tower on the reef began in 1848, supervised by Captain Howard Stansbury (at the time, U.S. Army and Navy officers were assigned as lighthouse inspectors).
Construction had originally been expected to be completed in a year, but funds had been held up while the U.S. Congress investigated the Lighthouse Service.
[14] The original light apparatus consisted of 18 lamps, each with a 21 inches (530 mm) diameter reflector.