The Oxus is an unusual river. It has no clear beginning or end. For centuries the river, which is also known as the Amu Darya, has served as the border between Afghanistan and Tajikistan.
The Oxus is the longest river in Central Asia, but no one knew where exactly in the mountains it originates. After coursing through 2,400 kilometres, it fizzles out downstream in the Kyzyl Kum desert, never reaching the sea.
Amateur British mountaineer Bill Colegrave and his team now say they have finally cracked the age-old mystery of the river's origins. In a recent book Halfway House to Heaven about their expedition to the Afghan Pamirs in 2008, they name a small stream as the Oxus' source.
Back in the 19th century, at least four teams of Victorian adventurers competed to identify the river's source. They came up with four different answers, which added a sense of mystery to the river.
Expeditions to the area stopped during the turbulent upheavals of the 20th century. The Oxus, which was already so difficult to reach, became further romanticised.
Colegrave, who enjoys travelling to remote corners of Central Asia, was mesmerised by the puzzle. When roads opened again in 2005, the avid explorer decided to give it a go. He teamed up with Irish amateur geologist Anthony Kitchin and Afghanistan expert Dillon Coleman. Their expedition approached the region from Tajikistan and proceeded to the upper regions of the Oxus in north-eastern Afghanistan on foot and horseback.