Jim Mann heads away from Pen-y-Pass at the start of the Snowdon horseshoe during the 2015 race. Photo: Ian Corless

More than 200 runners from 24 different nations are preparing to start one of Britain’s most gruelling races.

The Berghaus Dragon’s Back Race starts at 7am on Monday, with British ultrarunner Jim Mann defending his title after his 2015 victory.

Carol Morgan, fastest woman to complete the Montane Spine Race this January up the full distance of the Pennines, will also join the field, which includes Joe Faulkner, the only person to complete every Dragon’s Back since it was first held in 1992.

The event has only been staged three times previously, with the original race being re-run in 2012 and 2015. It follows a route down the mountainous backbone of Wales.

It is billed as the toughest five-day mountain race in the world and fewer than half of the runners who start are expected to complete the course.

The 2017 field is the biggest ever and includes some of the world’s very best ultrarunners.

Carol Morgan smashed the women's record in this year's Montane Spine Race. Photo: Bob Smith/grough

The Berghaus Dragon’s Back Race will start in the courtyard of Conwy Castle, after a performance by Maelgwn Male Voice Choir. The runners will then race out along the ancient town walls of Conwy before heading up to the Carneddau, Glyderau, Snowdon and beyond.

The public will be able follow the progress of the race thanks to live tracking via the Berghaus website.