CHARLESTON, S.C. (AP) — College students are going to help archaeologists map the walls used to defend Charleston more than 250 years ago.

Students from Clemson University and the College of Charleston will use ground penetrating radar in downtown Charleston's Marion Square to find exactly where the fortification called the Hornwork was built, the American Battlefield Trust said.

The 30-foot (9-meter) tall wall built in 1758 stretched for three city blocks and also had a ditch or moat. The wall was made from tabby, which was a mix of seashells, sand and lime, the organization said.

The Hornwor...