Swiss soldiers began guarding Vatican City in 1506.
At the time Swiss Cantons were very poor, and men started emigrating to other places in hopes of finding a better future. Most of the jobs available to immigrants were as soldiers. Swiss soldiers were seen as loyal, courageous, and hard-working, and as a result Pope Julius II invited them to protect him and the Vatican.
Although the world is generally a safe place, and strangers are often more kind and well-meaning than evil, there are locations where travelers typically shouldn’t venture, places ravaged by wars, terrorism, civil unrest, or violent crime.