WHAT WOULD Julius Caesar do in Iraq? "He'd win" is the simplest answer. How he would do it is harder to say — after all, just how would a man like that behave in the modern world? We can never know, but his campaigns in Gaul give us a fair idea.

When Caesar led his legions into Gaul — basically present-day France and Belgium — in 58 BC, many of the tribes there greeted him as a liberator. Six years later, almost all of them rebelled against him in a war fought with appalling savagery. Through skill and luck, Caesar won. He then spent the better part of two years in painstaking diplomacy. As one of his own officers put it: "Caesar had one main aim, keeping the tribes friendly and giving them neither the opportunity nor cause for war." It worked, and Gaul remained at peace when he left in 49 BC.

From the start, Caesar backed his campaigns with concerted and highly personal diplomacy. He met the tribal leaders as a council at least once a year and visited them individually more often. The great rebellion in 52 BC was all the more surprising because it was led by chieftains who had done very well out of their alliance with Caesar. They had decided that they would do even better if the Romans were expelled. Allies, and especially those in an occupied country, may not necessarily have the same long-term ambitions.

Of course, Gaul in the 1st century BC was a very different place from Iraq today. The many mutually hostile tribes of Gaul, divided by language if not religion, had never been combined into a single nation. Caesar came as a conqueror, the agent of a blatantly imperialistic Roman Republic that had already occupied much of the Mediterranean world. There was no talk of creating a free democracy, still less of exit strategies. Gaul would remain part of Rome's empire for more than five centuries.

Caesar was effectively a free agent because there was no way that the Senate could have directed events from Rome when messages took weeks to reach Gaul. He also combined supreme civil and military power in his office as proconsul, so that he both devised and implemented political and military strategy. There was a single mind and purpose behind Roman policy in Gaul. Despite his power, Caesar couldn't lose and get away with it. Failure would have meant exile or death. Put simply, Caesar could not afford to consider withdrawal.

Even without 24-hour news and an international community watching his every move, Caesar was acutely aware of the need to win over public opinion. Each winter he produced an account of the year's campaign, designed to be read aloud and to thrill an audience of Romans. From the beginning, these were acknowledged as one of the highest expressions of the Latin language.

The Bush administration has been far less effective in selling the war to the U.S. public, and Tony Blair's government has made even more of a mess of winning over domestic opinion in Britain. More seriously, from the beginning there were major errors in strategy. The coalition forces have performed superbly, but too few troops were sent, especially because insufficient attention was paid to reconstructing Iraq.

When Caesar suffered one of his few defeats and lost 1 1/2 legions in the winter of 54-53 BC, his response was to replace them with twice as many men. The idea was to show that Roman resources and determination were inexhaustible.

Caesar knew that soldiers could only do so much and that lasting peace needed a political settlement. In Gaul, the tribes were left to govern themselves in their day-to-day affairs — that was the Roman way. In the long term, the leaders would be absorbed into Rome's aristocracy. In the short term, they had to be treated fairly and persuaded that accepting Roman rule was more attractive than resorting to violence.

At times, Caesar was ruthless in ways that would and should be utterly unacceptable to the United States and its allies. One prominent chieftain who displeased him died "resisting capture." Another was publicly flogged and beheaded without the formality of a trial. These were misjudgments and helped provoke the great rebellion in 52 BC. Other brutal warnings of the price of opposing Rome were more effective — the defenders of one captured town had their hands cut off. Caesar also launched attacks on neighboring Germans and Britons because he felt that they threatened the peace in Gaul. Today he would presumably be more ready than seems sensible to make similar strikes on Iran or Syria.

Caesar made mistakes in Gaul, and came very close to defeat, but he never doubted his ultimate success. This was not just a question of staying the course. Caesar was able to admit when he had made a mistake. He adapted, changed his plans to meet a situation and threw every resource — including his own massive energy — into achieving his aim. In a few years in Gaul, initial victory turned to apparent disaster, and that was turned into lasting success.

Caesar's experience shows how a seemingly desperate situation can be salvaged, but it does not suggest that this is easy, and there is a lot about his example we would not want to follow. The time it took for Caesar to turn the situation around in Gaul shifted the political balance in Rome hugely in favor of his bitterest opponents. Victorious in Gaul, he still saw his career threatened with extinction. He didn't hesitate. He left Gaul to make war on his own country. Mavericks like Caesar make effective war leaders — but can be dangerous if a state fails to control them.