OLD TOWN ALEXANDRIA, Va. — Nestled in centuries of dirt and debris, several well-preserved ships and artifacts have been unearthed that offer a glimpse of life at what was once one of the busiest ports in the North American colonies. At the site for Robinson Landing, a new townhouse and condominium development along the Potomac River here, excavations have uncovered the protruding, curved wooden bones of the ships. Three ships were scuttled and buried here centuries ago as Alexandria sought to expand its land into the deeper waters of the river. “It tells us a lot about the resourcefulness of...