-- Is it possible to stage a simulated terror attack without tying up a city that is usually knotted by traffic chaos? Rome's answer, during a civil defense drill held Monday morning, was no.

Police staged three fake bomb blasts at picturesque downtown locations: the Coliseum; the Piazza della Repubblica, near the central train station; and Corso Vittorio Emanuele, a major boulevard that runs by the Piazza Navona.

In an effort to keep confusion to a minimum, a large triangle of central Rome was blocked off for two hours. Traffic diverted from entering the area created huge jams along the Tiber River and outside the old city walls as far away as the super-ring road that circles Rome's suburbs.

As a result, relatively few Romans -- unless they were home watching the live television broadcast -- witnessed either the false suicide mannequin explode on a crosswalk outside the Coliseum, the smoky little blast inside the Piazza Repubblica subway station or the virtual bus bomb on Corso Vittorio. City and central government officials said the scheduled drill was meant to test communication and evacuation routes, not engage the whole town in a reality show.

"We know well there will be inconveniences," Achille Serra, the central government's liaison at city hall, said before the drill. "Romans know it is all in their interest."

The exercise was the second in a series of four set for major Italian cities. Milan held one 10 days ago, and Naples and Turin are next. The July transit bombings in London impelled Italy to test its emergency response, officials said. The government has long warned that Italy is in the sights of terrorist organizations.

"It was a time test to see how the entire health and rescue sector would respond," said Vitiliano di Salazar, head of the country's civil protection agency.

The Coliseum scene included not only the test-bomb dummy, but also three pre-placed wrecked cars, one of which was set on fire. Dozens of firefighters and civil protection volunteers stretched out on the lawn and cobblestones around the ancient amphitheater, playing faux victims of the blast. Smoky fires burned in metal barrels in an attempt to add to the atmosphere. A steady rain added to a sense of gloom.

Firetrucks arrived fairly quickly, followed by ambulances to carry off the first ersatz wounded. But some sidewalk critics were unimpressed.

"It took rescuers 20 minutes to get here. They were too slow, and too late," said Gerard Kroscteinar, an Austrian tourist.

Carolina Vojteisek, 23, a university student in Rome, looked on and said the exercise was "only relatively useful, because all the trucks and rescuers were ready for it." She said, however, that she feared a terrorist attack on Rome, did not use the subway system and often felt nervous on buses.

But Bob Schwertfeger, a traveler from Rochester, N.Y., said: "It looks to me like they did a good job; they seemed to be organized. I think it's a good idea, a necessary exercise."

A moment of genuine alarm occurred when police found an unattended backpack at the base of one of the Coliseum's arches. A photographer returned to claim it before the bomb squad arrived.

Reality also briefly intruded at Piazza Repubblica's subway station, the site of the most complex drill. As some of the fake injured were carried on stretchers from below the street and others limped around the plaza, a woman at a nearby bus stop fainted for real. One of the ambulances ferried her to a hospital.

Over at Corso Vittorio, a theatrical protest by a clutch of antiwar demonstrators interfered with the mock bus explosion. The group of youths set off flares and a red smoke bomb, chanted "Peace now" and unfurled a banner that read, "Get troops out of Iraq." Italy maintains about 2,500 troops there.

Riot police on hand for the exercise formed a phalanx to drive the demonstrators toward Campo dei Fiore, central Rome's biggest outdoor market. A half-hour late, a little pop on a No. 64 bus signaled the simulated explosion. First-aid workers treated the mock wounded, some of whom puffed on cigarettes as they lounged on the pavement.

Carlo Minotti, an accountant, looked over the scene and judged it as too relaxed.

"They have to hold one of these by surprise, with the traffic included, and then see how things go. Does anyone think that if there was an explosion on this street, ambulances could reach here? They can barely pass on a normal day," he said.

Fires outside the Coliseum in Rome are part of a simulated terrorist attack. Blasts were staged at three sites downtown, where traffic was blocked for two hours. Firefighters in Rome carry a dummy during their response to a mock suicide bombing attack. Officials hope such drills, which will occur in two more Italian cities, will help increase response time in the event of an actual terrorist attack.