FORT EDWARD, N.Y. — Thanks to a blunder by crews dredging PCB-contaminated sediment from the Hudson River, archaeologists are learning more about the construction of what was once Britain’s largest fortification in North America.

An archaeological team is excavating the last visible remnants of Fort Edward, built along the river’s east bank during the French and Indian War. The experts were brought in earlier this month after crews accidentally tore out several wooden beams from the original fort while dredging sediment last month.

Archaeologists say more beams discovered submerged along the river bank are giving them a glimpse of how 18th-century military engineers constructed fortifications. The excavation is expected to be wrapped up next week.