Recently, the FBI revealed that it had arrested a 15-year-old Philadelphia-area boy on charges that he plotted to carry out Islamic State-inspired attacks involving explosives-packed pressure cookers (in the style of those used in the Boston Marathon attacks.) Although the plot never went beyond Internet chatter, the plan—targeting Pope Francis during his 25-27 September, 2015 visit to Philadelphia—highlights the nightmare that such a significant event can and does have on local, state, and federal law enforcement, the military, and the intelligence community. But just how much of a challenge does such a significant event pose?

To be fair, those whose job it is to protect the Pope and other persons of importance are true professionals and have the dance down pat, so this is in no way a bashing. Pope Francis is, as of the time of this writing, finishing up a visit to Cuba, then he will head to Washington D.C. before stopping in Philadelphia. The Philly visit is the final and largest portion of the 2015 World Meeting of Families (WMF), and according to the website, is “held every three years and sponsored by the Holy See’s Pontifical Council for the Family, the World Meeting of Families is the world’s largest Catholic gathering of families.” The words “world’s largest Catholic gathering of families” are enough to make any security detail leader, police chief, or counterterror operator cringe. (And no, not because they are Catholics, but because of the sheer number of people involved.)

So, for a little background on what Philadelphia and the surrounding areas can expect, let’s put some numbers on the screen (imagine my awesome 2nd lieutenant, up-all-night-to-please-the-general PowerPoint clicking away here). Philadelphia boasts a population of approximately 1,556,600, (according to a 2013 estimate) making it the second largest city on the east coast and the fifth largest in the United States. None of this counts the millions of tourists, business visitors, and other passers-by who trek to the city every week. The city hosts a diverse population, and equally diverse “islands” (those areas within a city—college, financial, ethnic, etc.—where anyone on a surveillance detection route can drag his/her potential followers out of hiding). Everything from the Italian Market to the numerous museums and the Liberty Bell, Philly brings them in droves. And thus the security nightmare is born. Oh, and did I mention that it is being billed as the largest security operation in the U.S. to date? Yeah….

Now, on to some of the physical measures that are already being put in place. And before anyone pulls the “Why are we talking about this? ISIS and OPSEC!” card, cool it. Everything talked about here is public knowledge and can be found if researched. The Ben Franklin Bridge, the main span across the Delaware River that separates Pennsylvania and New Jersey, will be shut down to all vehicular traffic from 10 p.m. Friday night until noon the following Monday. The only traffic allowed on the bridge will be on foot. There will be parking on the Camden, New Jersey side of the bridge, and visitors will be allowed to walk from there into Philly.