The African Burial Ground

National Monument built in lower Manhattan
The African Burial Ground in the city of New York is a graveyard that dates back to the 1650s, shortly after New York became New York. Before this site was discovered, information about slavery in that period was muddy at best but, due to the discovery of this site, more light has been shed on slavery and the African American community of the time.
Construction for a new federal building in Lower Manhattan began in 1987. Prior to construction in the early 1990s, surveys revealed the African Burial Ground. Initially, the discovery was thought to be much smaller, so the bodies were initially taken off-site before the General Services Administration (GSA) decided they needed an alternative approach. Many parties were interested in the site and its preservation, so the GSA stopped all work until they decided on a proper course of action.
The federal building design was changed to avoid disturbing or damaging the graveyard.
So What?
This site is significant because initial surveying only showed a small cemetery in the location, but with later surveying, they found an extremely significant archaeological site.