NEW YORK — Specialists using ground-penetrating radar have detected hundreds of previously undiscovered gravesites in an African-American burial ground that dates to the 1830s.

The New York Landmarks Conservancy announced the discovery Monday at Staten Island’s Rossville A.M.E. Zion Church Cemetery, part of the historic Sandy Ground community that was among the nation’s first free-black settlements.

Before the radar survey, there were 97 known burial sites, many marked by headstones, on the 1.6-acre burial ground. Conservancy President Peg Breen said another 576 were discovered by radar at an average depth of about 10 feet, bringing the number of total gravesites to 673.

“What we hope is that discovering the gravesites will bring the story of Sandy Ground back to life,” Breen said. “The story is very little known and deserves to be told.”

Sandy Ground, within walking distance of piers and docks, was settled by African-American oystermen escaping restrictive farming laws in the Chesapeake Bay. More than 150 families eventually moved there and prospered, owning their own homes, businesses and property. The current Zion Church, which dates to 1897, was a major stop on the Underground Railroad for escaped slaves.

By 1916, the oyster beds had become depleted and were closed. Fires in 1930 and 1963 destroyed much of the settlement.