The massive stone wharf loomed over Rio de Janeiro’s harbor, serving as the arrival point for nearly a million enslaved Africans during the first half of the 19th century. Today, the ruins of the Valongo Wharf are the only physical remains of a slave trade port left standing in the Americas.

On July 9, the United Nations Educational, Scientific and Cultural Organization (UNESCO) named Valongo Wharf a World Heritage site, along with northwest England’s Lake District, the walled city of Ahmedabad in India and the sacred Japanese island of Okinoshima, which doesn’t allow women on its shores. 

Of the new sites on the list, none has a darker past than Valongo Wharf. Built in 1811, the wharf functioned as South America’s leading slave port. It was here that as many as 900,000 enslaved African men, women and children were held before being sold on the Brazilian slave market. Those who didn’t survive the ordeal—who died during the transatlantic journey or sometime after arriving at the wharf—were buried in mass graves nearby.