Border Trade.
Face off: Taliban fighters and Pakistani soldiers guard the busy Torkham border crossing side by side
The Khyber Pass is one of the world's great invasion routes - forbidding, steep and treacherous, stretching from the Afghan border to the Valley of Peshawar, 20 miles (32 km) below, in Afghanistan.
For three thousand years, armies have struggled through these rocky defiles and camped in its valleys. You can still see the insignia of regiments from the British and British Indian armies, which continue to be carefully maintained, along the sides of the road, overlooked by the forts they once built and guarded. From the rocks above, Pashtun tribesmen armed with ancient jezails, or flintlock rifles, would snipe at passing soldiers with amazing accuracy.
Nowadays trucks laden with agricultural produce from Afghanistan labour round the sharp bends, sometimes with men and boys clinging to the side of them for the ride. On the pathways beside the road, old men trudge along, bent double under boxes of smuggled goods.
'An atmosphere of fear and urgency'
The Khyber Pass ends at Torkham - Afghanistan's busiest border crossing with Pakistan.
Several years ago the Pakistani authorities completely revamped it. Now the crowds waiting there are better marshalled than they used to be, but there's an atmosphere of fear and urgency as people try to escape from Afghanistan's new rulers, the Taliban. You can see them from the Pakistani side, crowding together behind the wire in the midday heat, waving their documents and begging to be allowed through. For the most part, only people who have permission to leave Afghanistan on medical grounds can cross, together with their families.
The long line, cluttered with wheelchairs and suitcases, shuffles slowly forward through the various checkpoints.
Taliban and Pakistani guards may work relatively peacefully at the border - but they are not friends
On the road, where the actual border runs, a couple of Pakistani soldiers stand face to face with Taliban guards wearing makeshift uniforms.
The Taliban had no objection to talking to me. I asked one of them, a big man with a bushy beard covered by a face-mask, why the national green and red flag of Afghanistan wasn't flying over the border post. It has been replaced by the white flag of the Taliban, inscribed with the Shahada, the basic statement of the Muslim faith: "There is no god but God, and Muhammad is His messenger."
"Our country is now an Islamic Caliphate," the border guard answered proudly, "and this is the correct flag for the whole country."
John Simpson and his team interview a Taliban border guard