At Unz.com Steve Sailer points out
It appears that one terrorist strategy is to hit extremely famous spots (such as Westminster Bridge next to Big Ben, or the defeated assault on the Louvre) to disrupt tourism.I hear the Eiffel Tower will soon be surrounded by a glass wall.
I hope St. Peter’s Basilica has extra security. Is that the most famous place in Europe?
As we learned when the Pope attacked Trump's proposals to put a wall on the Mexican border as un-Christian, St. Peter's is the best guarded landmark in Christendom
It's a sovereign state, not apparently subject to EU immigration or refugees rules, has its own walls, and is guarded by the Swiss Guard, who are extremely well armed.
Here's what that "American Veteran" letter said
To my professional eye it appeared an infantry company minus was on duty around the Vatican City perimeter. I expect the remainder of this unit's parent infantry battalion was located nearby and ready to reinforce at short notice.Inside Vatican City we only saw two Swiss Guards in their traditional ceremonial uniforms. These were at a portico under St Peters. The rest of the Swiss Guards were in their simple duty blue uniforms. All of them were packing pistols. Plenty of armed Vatican City police were visible, too.Whatever public hypocrisy Francis and his minions indulge themselves with about immigrants, walls and border guards, he and his hierarchy clearly regard themselves as being under constant direct threat of lethal violence originating from "migrant" people who are alien to the Vatican City state.
The Vatican hierarchy may support mass immigration, but it doesn't expect to experience it.