Papal bodyguards on Wednesday overcame a man who tried to board Pope Benedict XVI's open white jeep carrying the pontiff through St Peter's Square.
The man jumped over a barricade and tried to leap on to the back of the vehicle as the pope was riding through a crowd of some 30,000 pilgrims at the start of his weekly general audience.
The pope, standing up behind the driver, was apparently oblivious to the incident, continuing to wave to the pilgrims.
The Vatican-watching news agency I-Media said Swiss Guards immediately arrested the man, who was wearing a pink T-shirt, black shorts and a green baseball cap, calling him "mad" and probably a foreigner.
Italian police told I-Media that Vatican police took the man in for questioning and would then hand him over to Italian police detailed to Vatican security.