The Vatican is seen as the heart of the Christian world, but some also eye the international iconic symbol of Christianity (search) as a terror target.
"I think the Vatican has to be considered a target because Al Qaeda has said that the Vatican is a target," said Kishore Jayabalan, a former Vatican official, now of the Acton Institute. "One of the things the Vatican has tried to do is to downplay the differences between Islam and Christianity."
In the past, messages released by terrorists often express desire to attack Jews, Christians and Western countries. Some experts see this and the church's influence on Western Civilization as a sign of the Vatican's vulnerability.
But the Rev. John Wauck of the Pontifical University of the Holy Cross Foundation is not convinced terrorists seek to bring down his religion.
"Terrorists of today are not interested in attacking Christianity per se. The pope himself has said that the target isn't Christianity as such. But they're interested in attacking Western Civilization," he said.
Aside from its symbolic importance, the Vatican is seen by some as a potentially strong temptation for terrorists simply because it attracts so many tourists. The Vatican's museums had more than 3.5 million visitors last year.
This summer, a record 23,000 people visited in a single day.
Before the Sept. 11, 2001, attacks on the United States, the police presence at St. Peter's Basilica (search) was strong due to terror threats in the Jubilee Year of 2000. Vatican police are on even higher alert now, although keeping a low profile, with most of the police in plain clothes, according to security experts.
Click in the box near the top of the story to watch a report by FOX News' Greg Burke.