Three friends have set off on a 39-marathon run through nine eastern European countries to raise funds for the victims of child trafficking.
Tom Stancliffe, Guy Hacking and Rob Martineau will face the threat of wild dogs in Bosnia, endure freezing nights in the Ukraine and snow storms in the mountains of Montenegro as they cover some of the continent's most remote terrain.
The trio aim to complete their 1,036-mile challenge in just 33 days and will spend most nights sleeping rough in villages.
Their mission winds through countries known for people-trafficking, including Moldova, Romania, Bulgaria, Macedonia, Montenegro and Kosovo - where they will complete their longest stretch of more than two marathons in a day.
The three men set off from Odessa in the Ukraine, carrying their supplies on their backs. They will have to complete the run without the assistance of support vehicles or medical aid, but around 200 runners from across Europe plan to join them at points along the route, giving them a boost when energy levels dip.
Mr Stancliffe, 27, a lawyer from Kennington, south London, said: "We will have to run through the pain barrier and can't slow down for sore knees, sprained ankles, severe blisters or stomach upsets.
"If we can survive a really tough first week running along the Black Sea in Ukraine and into Eastern Romania then we hope our bodies will get into the rhythm of running more than a marathon a day for over a month."
Mr Martineau, 26, a travel writer from Jericho, in Oxford, added: "It's going to be a great adventure for us and although we're all a little nervous about the challenge, we've trained hard and we're eager to hit the road.
"It's been so exciting to see so many runners from across Europe, many of whom we don't know, joining us and we can't wait to meet everyone along the journey."
The trio will stop to meet charities and politicians in the cities of Bucharest in Romania, Sofia in Bulgaria and Pristina in Kosovo. They aim to raise £150,000 to enable trafficking charity Love146 to build Britain's first residential trauma recovery centre for children.