New York City (nee New Amsterdam) was mostly a farming community in the century-ish before the American Revolution. The slaves on those farms were allotted a space in the no-man's land just north of the city proper to bury their dead; the area is believed to span about seven acres in what is now Lower Manhattan, near City Hall. Between construction, the building of the subways and the building of roads, most of the grave sites were obliterated over the centuries.
When the skeletons were discovered in 1991, there was an uproar from the community about how to respectfully deal with the remains - not to mention an uproar from developers who wanted to build on the site. Eventually, a compromise was reached, which included designation of the site as a National Monument and the ceremonial re-burial of the recovered skeletons after archaeological review.
The monument is especially cool because it's so new, I think. The visitors' center is very cool, with tons of information about the history of slavery in New York City. An informational video is re-created with spookily realistic life-sized sculptures of the actors in the film. After studying African-American and post-colonial literature out the wazoo in college, it was really cool to visit this site and increase my knowledge.
i wuz heer.
Find 9 more images below the jump, including the visitors' center as well as the outdoor memorial.