Europe in ancient times - we have the history.
In ancient Rome, a strip of open land along which troops advanced into unfriendly territory. It came to mean a Roman military road, fortified with watchtowers and forts. An example of this construction was the continuous system of fortifications and barriers extending 345 mi (555 km) along the Roman frontier in Germany and Raetia. Hadrian's Wall also served as a limes. Though not impenetrable, the limites allowed the Romans to control communications along frontiers and deterred raiding parties. In the eastern and southern empire, limites were often used to guard caravan routes.
Find more information on limes. Upgrade to Britannica Online for more on limes.