frontier

…Wall was the most impressive frontier work in the Roman Empire. Despite a period in the following two reigns when another frontier was laid out on the Glasgow–Edinburgh line—the Antonine Wall, built of turf—the wall of Hadrian came to be the permanent frontier of Roman Britain. The northern tribes only…

…“especially in the United States,” the term referred to that “belt of territory sparsely occupied by Indian traders, hunters, miners, ranchmen, backwoodsmen and adventurers of all sorts” which formed “the temporary boundary of an expanding society at the edge of substantially free lands.” Others have thought of it as “a…