In 122 CE, Hadrian, the Roman emperor, drew a line in the sand, and set limits to the size of the Roman Empire.
This step was necessary as the Empire had become increasingly unwieldy to administer. Instead of throwing even more money, and yet more troops at the problem, as many suggested, Hadrian determined on a different solution.
Boundaries were marked around the Empire, and although the walls and defensive works that he ordered to be built, did serve a military purpose, the main idea seems to have been to control what came in, and what went out of the Empire.
For many of us, deciding what we allow into our inner world is a major problem.