The world's most prestigious mountain race kicks off from Chamonix at 6pm (France time) today. Several build-up races have already taken place, but the Ultra Trail du Tour du Mont Blanc is what the eyes of the trail running world are fixed on.
Here are the facts and figures that make the 2017 UTMB so special:
2 The number which will be worn by Kilian Jornet - the undisputed king of mountain running. He'll be up against two previous two-time winners in Xavier Thevenard and François d'Haene.
3 The number of countries covered - beginning in France, the race also goes into Switzerland and Italy.
21 The number of hours the first runners will be expected to take.
46.5 The cut-off point for the slower runners (46 hours 30 minutes).
59 The age of Italy's Marco Olmo when he won this race for the second time in 2007.
171 The distance in kilometres to be run (all in one stage). That's more than 106 miles and just over four marathons.
2300 The maximum field size.
2500 The highest altitude anywhere on the course.
10,000 The approximate number of metres of ascent/descent - about the same as going up the Pyg track from Llanberis to the peak of Snowdon 12 times.
Follow the race live at http://utmbmontblanc.com