On the ground, bus and rail are the primary travel options. Sochi hugs the Black Sea for 92 miles, and there are only two main arteries into the city: one highway and one rail line. By road, the nearest intersection is 100 miles northwest of Sochi along the winding M27 highway, through villages and mountain switchbacks. And as of Jan. 7, drivers with out-of-town license plates have had to leave their cars 60 miles away and take shuttle buses in.

The rail line winds up the coast some 75 miles to the town of Tuapse, then splits off through mountains and into one of Europe’s largest primeval forests. Beyond that point, a spider web of transport hubs, connecting railways, and sleepy stops in towns and tiny villages links Fortress Sochi to the city of Krasnodar and the rest of the world. Of course, Winter Games are often held in hard-to-reach mountain towns, but the journey to Lake Placid, Nagano or Lillehammer did not wind through terrorist stomping grounds.

Both of these fragile ground-transport ribbons are vulnerable to attack. A well-placed obstruction on a hairpin turn would delay traffic for hours. Combined with a terror strike, it would decimate any sense of safety at the Games, cast a pall over Sochi and shake Putin’s image as a man with an iron grip. Blast roadways and train tracks simultaneously, and one of the largest sporting events in Russia’s history becomes a disaster.