One evening in the fall of 1991, it was raining, and the traffic was heavy, so I turned on the radio and settled in for a slow ride home. When I heard NPR report that an excavation crew for a new Federal Building in lower Manhattan had unearthed several skeletons of African slaves, I wasn’t surprised. Every American colony had slaves. Of course New York had its share. But the numbers astounded me: Before the abolition of slavery in New York in 1827, about 20% of the city’s population was black. One slave cemetery, now beneath Manhattan’s roads and buildings, holds at least 15,000 corpses.

By investing in southern plantations, military suppliers, and big corporations, New York City got so rich on the “peculiar institution” that on the eve of the Civil War, Mayor Fernando Wood proposed secession rather than lose cotton trade with the South.

Few New Yorkers today know that slaves built lower Manhattan, including the wall that once defined Wall Street. By midsummer 2015, the city will try to rectify this ignorance by installing a 16-by-24-inch plaque near where an open-air slave market was erected in 1711. This busy and lucrative market became “the geographical birthplace of American capitalism.” (NY Times, May 8, 2015).

The plaque is good idea but will do little to make visible the invisible black people who, on their backs, carried New York City and the whole of the United States to prosperity, strength, and world prominence.