Under blue tents in Cockeysville, archaeologists scrub shards of pottery with toothbrushes. Nearby, small flags jut from the grass and a hole reveals a stone foundation and steps.

It might seem an unlikely place for an archaeological project, just a short distance from Interstate 83 and a light rail stop. But it's where a team of archaeologists working with the Maryland State Highway Administration is unearthing the remnants of a small plantation where slaves, free blacks and European immigrants once labored side by side, an arrangement historians say was more common in Maryland than in other slave states.