IN 2000, GREG MORTENSON and I hatched the idea of traversing the length of the Wakhan Corridor, the thin, vestigial arm of northeastern Afghanistan that extends eastward to the border of China, separating Tajikistan from Pakistan. As founder and director of the Bozeman, Montana–based Central Asia Institute (CAI), a nongovernmental organization that has built more than 50 schools in the tribal borderlands of Pakistan and Afghanistan, Greg had plenty of experience navigating the region's dicey political landscape.

We were planning to go in the fall of 2001. Then, on September 9, Ahmed Shah Massoud, commander of Afghanistan's anti-Taliban Northern Alliance, was assassinated by Al Qaeda suicide bombers. Two days later, 9/11. A month later, American cruise missiles were detonating on Taliban positions. Within half a year, the war in Afghanistan was putatively over, but it wasn't. It's never over in Afghanistan.

Afghanistan is a palimpsest of conquest. The Persians ruled the region in the sixth century b.c., then came

For decades, no one had traversed the entire length of the Wakhan, following the old Silk Road from the northward bend of the Panj River to the far end in Tajikistan. We had no idea if it could be done.

Alexander the Great 200 years later. The White Huns in the fourth century a.d., Islamic armies in the seventh, Genghis Khan and the Mongols in the 13th. It wasn't until the 18th century that a united Afghan empire emerged, then came the British, then, in 1979, the Russians. And now the Americans and their allies.

In October 2004, Afghanistan elected President Hamid Karzai, but his control barely extends beyond Kabul. As it has been for centuries, the Afghan countryside is ruled by tribal and regional leaders. It's a complex power network fraught with shifting allegiances. In the eighties, Afghan mujahedeen ("freedom fighters") were armed and funded by the CIA to resist the Russians. After the Soviet occupation ended, in 1989, Afghanistan plunged into a state of internecine fighting: Warlords—regional leaders backed by independent militias—clashed, and the country fractured into a patchwork of fiefdoms. In 1996 the Taliban, a generation of Afghan Islamic fundamentalists that had grown frustrated with civil war, seized control of Kabul. They subsequently gave safe haven to Osama bin Laden and his Al Qaeda fighters. Today, despite the presence of 33,000 NATO and coalition troops, Afghanistan remains a violent, dangerous mess.

If any region of the country stands apart, it's the remote, sparsely populated Wakhan Corridor, which has been spared much of the recent bloodletting. Carved by the Wakhan and Panj rivers, the 200-mile-long valley, much of it above 10,000 feet, separates the Pamir mountains to the north from the Hindu Kush to the south. For centuries it has been a natural conduit between Central Asia and China, and one of the most forbidding sections of the Silk Road, the 4,000-mile trade route linking Europe to the Far East.

The borders of the Wakhan were set in an 1895 treaty between Russia and Britain, which had been wrestling over the control of Central Asia for nearly a century. In what was dubbed the "Great Game" (a term coined by British Army spy Arthur Conolly of the 6th Bengal Native Light Cavalry), both countries had sent intrepid spies into the region, not a few of whom had been caught and beheaded. (Conolly was killed in Bokhara in 1842.) Eventually Britain and Russia agreed to use the entire country as a buffer zone, with the Wakhan extension ensuring that the borders of the Russian empire would never touch the borders of the British Raj.

Only a handful of Westerners are known to have traveled through the Wakhan Corridor since Marco Polo did it, in 1271. There had been sporadic European expeditions throughout the second half of the 19th century and the beginning of the 20th. In 1949, when Mao Zedong completed the Communist takeover of China, the borders were permanently closed, sealing off the 2,000-year-old caravan route and turning the corridor into a cul-de-sac. When the Soviets invaded Afghanistan in December 1979, they occupied the Wakhan and plowed a tank track halfway into the corridor. Today, the Wakhan has reverted to what it's been for much of its history: a primitive pastoral hinterland, home to about 7,000 Wakhi and Kirghiz people, scattered throughout some 40 small villages and camps. Opium smugglers sometimes use the Wakhan, traveling at night.

In 2004, American writers John Mock and Kimberley O'Neil crossed much of the Wakhan, exiting south into Pakistan. As far as Greg and I could find out, for decades no one had traversed the entire length of the Wakhan, following the old Silk Road from its entrance at the big northward bend of the Panj River all the way across to Tajikistan. We had no idea if it could even be done.