The pope was not hurt and didn't even appear to notice that the man - who was between 20 or 30 years old - had jumped over the protective barricade in the square and toward the white popemobile as it drove by with the pope waving to the audience.
At least eight security officers who were trailing the uncovered popemobile as the pontiff passed by grabbed the man and wrestled him to the ground. The pope didn't even look back.
A Vatican official, who was not authorized to speak on the record, said the man was being held for questioning by Vatican police. He said the man had gotten as far as the back of the pope's white jeep before being wrestled to the ground, although video footage of the incident did not show clearly whether he actually made it onto the jeep.
The man, whose nationality was unknown, was wearing a pink T-shirt and dark shorts, a beige baseball cap and sunglasses. He appeared to have vaulted himself up and over the barricade from the second or third row back.
The jeep kept moving, Benedict kept waving and then proceeded with the audience as if nothing had happened.