A remarkable feat was recently completed in the heart of the Mont Blanc massif. Antoine Mesnage, a French tightrope walker and mountaineer, balanced on an 800-meter-long slackline hanging between two iconic peaks: the Dente del Gigante (4,014 meters), on the Italian-French border, and Mont Mallet (3,998 meters), in French territory. Mesnage, a highline specialist (an extreme variation of the slackline used at very high altitudes), walked on a rope only 19 millimeters thick, suspended 700 meters above the ground. Favorable weather circumstances enabled the tightrope walker to complete the crossing on what is the shortest route between the two peaks, but certainly not the least impressive. "It's the commitment that's scary", Mesnage told France 3. "You're on a lengthy line, where rescue is nearly impossible and breathing becomes tough. It's a condition of complete concentration, where you push yourself beyond your boundaries." The satisfaction, he noted, comes only later: "When you find yourself in your tent, in the evening, and you can finally say to yourself: 'Okay, I did it.'" Behind the outstanding individual accomplishment came a similarly impressive team effort. The project was carried out by the team 'Passagers du vide' (Passengers of the Void), a group of fifteen people who, after a month of preparation, transported and installed 400 kg of high-altitude equipment to ensure the crossing's safety.  A challenge at the limits of the possible—between mountaineering and the art of balance—that leaves you breathless.