So in 1991, when during construction of a General Services Administration office building in Lower Manhattan, graves were discovered 24 feet below ground, and when those remains led to the discovery of hundreds of other bodies in the same area, and when it was determined that these were black New Yorkers interred in what a 1755 map calls the “Negros Burial Ground,” the earth seemed to shake from more than just machinery. The evidence created a conceptual quake, transforming how New York history is understood and how black New Yorkers connect to their past.

That is a reason why Saturday’s opening of the African Burial Ground Visitor Center, near where these remains were reinterred, is so important. Among the scars left by the heritage of slavery, one of the greatest is an absence: where are the memorials, cemeteries, architectural structures or sturdy sanctuaries that typically provide the ground for a people’s memory?

The discovery of this cemetery some two centuries after it was last used provided just such a foundation, disclosing not just a few beads, pins and buttons, but offering the first large-scale traces of black American experience in this region. Here, underneath today’s commercial bustle, are tracts of land that for more than a century were relegated to the burial of the city’s slaves and free blacks.

In all 419 bodies were discovered — giving a clue to how many others still lie under the foundations of Lower Manhattan. (Estimates have ranged from 10,000 to 20,000.)

The new visitor center, inside the federal building that was ultimately constructed over a portion of the excavation (the other part became a burial site and memorial), is meant to explain the site’s significance — not a simple task, because the passions stirred by the discovery were not just historical, but also personal. There was a felt connection to the people, unearthed in their disintegrating coffins, who in the early decades of the city’s settlement were often forced into its construction. A sacral regard for the dead was joined with a sense of identification and continuity.