John Bowman, CBC News Online | December 2001
Tora Bora is a system of tunnels and chambers carved out of existing caves in the icy White Mountains southwest of Jalalabad, in the eastern part of Aghanistan, near the border with Pakistan.
It is one of the places where Osama bin Laden and Taliban leader Mullah Mohammed Omar are rumoured to be hiding.
The name Tora Bora is borrowed from a nearby Pashtun village and has been translated as "black dust" or "black widow."
The tunnels themselves were constructed 20 years ago during the Afghan conflict with the Soviets, with financial assistance from the Americans.
Because Osama bin Laden's family has a background in construction, it has been suggested he may have been involved in building the tunnels, as well.
The chambers are heated and ventilated, and gas-powered generators provide electricity. The complex is also thought to serve as a depot for ammunition and supplies for al-Qaeda forces.
There may also be an arsenal of American "stinger" surface-to-surface missiles at the base, left over from the Soviet war.
In 1996, after the United States pressured Sudan to expel bin Laden, he fled with his family to the former mujahadeen base at Tora Bora.
Geography plays a large role in the fortification. The only way to reach the complex over land is by horse, through the dense forests surrounding the mountains. The tunnels open onto sheer cliffs and are accessible only by mule trails on the cliff face.
From the air, the base is virtually impregnable. The cliffs, valleys and overhangs protect its entrances from aerial bombardment.
The caves themselves are built deep inside the mountains, so the American "bunker buster" bombs, which penetrate 30 metres into the earth before exploding, aren't very effective.
The Pentagon admitted that even the massive, seven-tonne "daisy-cutter" bomb dropped on Tora Bora on Dec. 10 was mostly for psychological effect.
"The reverberation effect that goes up those caves should have some kind of negative effect," said Pentagon spokesman Rear Admiral John Stufflebeem.