Slave port in Rio sparks debate

Experts hail historical site as one of a kind on American continents

The first few times American landscape architect Sara Zewde visited Rio de Janeiro's Valongo Wharf, she struggled to comprehend the recently unearthed remnants of what was once among the biggest slave ports in the world.

Excavated starting in 2011, the site is largely inscrutable, even to the trained eye: The spot where more than a half million enslaved African men and women debarked after harrowing journeys across the Atlantic is an open archaeological pit containing a jumble of paving stones.