Before their empire fell, the Romans built walls.
They began by erecting barriers along the border following the death of the Emperor Trajan in 117 A.D., notably Hadrian's Wall, which belted Britain. Later emperors erected internal walls, even around the great city itself, to ward off barbarians. After 300 A.D., the Emperor Diocletian effectively converted the entire Roman populace into feudal serfs, walling them off from internal movement in a vain effort to stabilize the chaotic economy.
Despite the cautionary tale of Rome, building walls, both literal and figurative, has remained a habit of great powers in decline -- the fateful course taken not only by Ming China, but also Soviet Russia, and even Great Britain.
Sadly, many Americans are all too eager to repeat history.
Witness the immigration bill slowly making its way through Congress, and the feverish reactions it has inspired. In exchange for granting undocumented workers a path to citizenship, Republicans have demanded a so-called "border surge" that would double the number of patrol agents in the Southwest and build an extra 700 miles of fencing. Due to bipartisan prejudice against so-called "low-skill" migrants, the legislation is also loaded with dangerous new government controls over the labor market. The Senate bill, for example, requires employers to post new jobs on a Labor Department website, certify that no citizen is displaced, and surrender wage-setting to bureaucrats. Nevertheless, the conventional wisdom is that the bill will open a floodgate of foreigners. The Heritage Foundation issued an outlandish warning about the supposed multi-trillion-dollar fiscal burden of new immigrants, practically suggesting that the Statue of Liberty be melted down for the border fence.