The Erie Canal

A canal is a dug waterway, and before the railway, water transport was the only cheap way to move heavy goods overland. The canal decided which east coast city became the continent's commercial centre — Philadelphia and Baltimore had no comparable route through the Appalachians. It also tied the Midwest economically to the northern states rather than southward down the Mississippi, which mattered when the question of union or secession arose a generation later. Construction was mocked as "Clinton's Ditch" and was paid off in nine years.