Excerpts from an Op-ed piece by John Arquilla, a professor of defense analysis, in the San Francisco Chronicle:

It isn't easy being great. Just look at ancient Rome, the most successful empire the world has ever seen, thanks to its superb military.

But the idea of an orderly Pax Romana is an historical fiction. For at the height of its power, Rome still engaged in almost constant warfare. Even the peace-loving philosopher-emperor Marcus Aurelius spent most of his time fighting against tribal raiders and outbreaks of terror on the frontiers. His "Meditations'' were almost all written in camp.

Sound a bit like our own situation?

[... all the threats to the U.S. ...]

We'd better come up with some other strategic options. In doing so, it may prove useful to recall how Rome, the greatest power of the past, coped with major threats.

Our own situation looks much like Rome's when the Empire was at its zenith in the second century. Rome then had no major enemies, but was beset by constant threats and warfare on the edges of its vast imperium.

At the political level, Rome sought not to alienate but to attract. It cultivated allies to share burdens, negotiated with enemies, and embraced their cultures. The 18th century historian Edward Gibbon slyly noted the Romans' intellectual suppleness in assessing all religions to be "equally true, equally false, equally useful."

Militarily, Rome's strategy was to cap the empire's commitments. With an ocean to the west, trackless deserts on the south and wide mountain ranges on the east, only the north was wide open. But instead of trying to keep on conquering in that direction, the Romans simply walled off Scotland, then drew lines at the Danube and Rhine rivers and secured the banks with forts and patrol flotillas. The system worked for centuries.

When Rome finally fell in 476, it was due to the failure to transform the legions from infantry to mounted forces capable of countering the nomadic horse archers who eventually brought down the Western Empire.

In the eastern half, though, the Byzantines did rebuild their military with heavy cavalry, and Constantinople outlived Rome by a thousand years. Not a bad payoff.

Can we now do as the Romans did? Of course we can, but we'll have to start by behaving as pragmatically as the Romans did. If we muffled our rhetoric about spreading democracy, the world would breathe a huge sigh of relief. If we focused on diplomacy and deterrence in dealing with Iran and North Korea, we could avoid war with them. Our willingness to withdraw from Iraq would be a powerful signal to the Muslim world that we do not seek a clash of civilizations.

There's no way to avoid all military commitments. The demilitarized zone between the two Koreas is the modern counterpart to Hadrian's Wall. Our navy must secure the Taiwan Strait and other critical sea passages, much as Roman flotillas once patrolled the Rhine, the Danube and the Mediterranean Sea. Even our continuing hunt for terrorists carries echoes of the occasional Roman forays outside the empire to root out bandit havens.

These are all clear-cut tasks that can be undertaken at reasonable cost. If we limit ourselves to them, rather than try to manage an essentially ungovernable world, we may be able to enjoy a Pax Americana even longer than ancient Rome's peace. If we keep pushing aggressively forward, however, we are bound to fail at ruinous cost. The choice is ours.