With simulated blasts outside the Colosseum, in a bus near Piazza Navona (search) and in a downtown subway station, Italians on Monday prepared for the possibility the Eternal City may be the target of a terrorist attack.

More than 500 police took to Rome's streets in the second in a series of anti-terrorism drills as helicopters whirred overheard and ambulances snaked through morning rush hour traffic. Another is still to come in Turin — the site of the 2006 Winter Olympics in February.

Italy raised its security alert after the July 7 homicide bombings on London's transit system, stepping up measures at airports, government buildings, foreign embassies and monuments. Premier Silvio Berlusconi's government has also said it is taking seriously purported threats by Islamic militants on the Internet, who say Italy — like Britain — could be attacked because it has troops in Iraq.

The drill began with a simulated suicide bombing outside the Colosseum (search). The area had been previously cordoned off, so there were no passers-by around.

Shortly after, firefighters and other rescue teams wearing yellow vests reading "drill" worked in heavy rain to put out fires and deal with feigned casualties near the ancient monument.

The government's top official for Rome, Prefect Achille Serra (search), said he was pleased with the drill.

"We found some problematic points. We can cut (our reaction time) by a few minutes but overall I am very satisfied," Serra said.

The Colosseum drill was followed 10 minutes later by a simulated explosion on a train at Rome's deepest subway station, Piazza Repubblica, where officials evacuated passengers from the train and escorted them above ground as smoke poured out of the station.

A third drill was performed with a controlled explosion of a backpack left on a No. 64 bus near Piazza Navona, a square in central Rome usually packed with tourists. The bus — usually filled on its route from the central station to the Vatican — was made to crash into two cars as part of the exercise.

In all, there were around 25 simulated deaths and more than 120 simulated injuries.

Observers included Marcello Segre, a spokesman for Turin's Red Cross (search). "It is useful to carry out drills in difficult situations such as the subway, with so many people and forces involved," he said.

But Agnese Marezzo, 60, who works in an ice cream kiosk in downtown Rome, said it was a mistake to disclose reaction details. "How we deal with a potential emergency should remain secret," she said.

The drill at Piazza Navona started 16 minutes behind schedule because of a demonstration at the site by anti-globalization protesters, who said removing Italian troops from Iraq would end the risk of attack.

Italy has recently pulled out 300 soldiers from its 3,000-member military mission, but government officials say the force will remain as long as needed by the Iraqis.