Palestinians and their supporters are running the West Bank's first marathon.
Itidal Abdul-Ghani, of the Palestinian Olympic Committee, said some 1,000 people are participating in Sunday's race - which includes shorter 10km and 20km options.
The marathon, taking place in cool, rainy weather, loops four times around Bethlehem, the traditional birthplace of Jesus.
Mr Abdul-Ghani says that because of Israel's separation barrier surrounding parts of the city, and its control over nearby land, there is not enough space to do a straight 26.2 mile run.
Israel says the barrier is needed to keep out attackers. Palestinians say it is a land grab.
The marathon comes six days after the Boston Marathon bombings and coincides with the London Marathon.
Some runners wore shirts honouring the Boston Marathon victims.