The largest collection of slave-ship shackles ever found on one site are part of the 20,000 artifacts uncovered from the British slaver Henrietta Marie, which is wrecked 30-feet underwater off the coast of Key West, Florida.

The Henrietta Marie is the only sunken slave ship in the world to be scientifically documented and one of only 10 slave ships ever discovered, according to The New York Times. In 1972, the Henrietta Marie was originally discovered by a group of treasure salvagers, which included a black underwater treasure hunter.

The Henrietta Marie, 80 feet long and 120 tons, left London in September 1699, according to a newspaper report from the time. It set a course for Africa's Guinea Coast, which ran from what is now Sierra Leone to Lagos in Nigeria. It would likely have taken about three months to get there.

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According to accounts from the 1600s of slave ship captains and owners, slavers would anchor their ships six or seven miles off the coast and, using the ship's longboats and hired African canoes, head into the interior, by river, to raid villages and claim their human booty.

Captured in raids or sold outright by African slave owners and traders, the men, women and children would have their mouths bound with oakum - a type of loosely twisted rope - and be tossed into the bottom of the boats offshore. Many others drowned when they were tied together like so many logs and floated out to waiting slave ships.

In 1993, members of the National Association of Black Scuba Divers placed a one-ton monument on the site of the slave ship to commemorate the African people who died aboard the Henrietta Marie and those lost during the Middle Passage. Today, the monument is the only underwater memorial of its kind in the nation.

A bronze plaque is embedded on the concrete monument. The inscription
reads: "Henrietta Marie: In memory and recognition of the courage, pain and suffering of enslaved African people. Speak her name and gently touch the souls of our ancestors."

The black divers take annual pilgrimages to the wreck of the Henrietta Marie. The site is protected by several federal marine agencies.

In June 2005, NABS members took a group of public school students to the Henrietta Marie site, marking the first time black students had visited the wreck. An 11-year-old student from Nashville became the youngest diver to tour the Henrietta Marie.

Artifacts from the Henrietta Marie are on display at the Mel Fisher Museum in Key West, Florida.