Khyber Pass, mountain pass in western Asia, the most important pass connecting Afghanistan and Pakistan, controlled by Pakistan. The Khyber Pass winds northwest through the Safed Koh near Peshāwar, Pakistan, for about 48 km (about 30 mi) to Kābul, Afghanistan, varying in width from 5 to 137 m (15 to 450 ft). The mountains on either side can be climbed only in a few places. The pass is walled by precipitous cliffs that vary in height from about 180 to 300 m (about 600 to 1000 ft). The pass reaches its highest elevation (1,072 m/3,517 ft) at the border between Afghanistan and Pakistan. For centuries the Khyber Pass was used by invaders to enter India. During the Afghan Wars the pass was the scene of numerous skirmishes between Anglo-Indian soldiers and native Afghans. Particularly well known is the battle of January 1842, in which about 16,000 British and Indian troops were killed. The British constructed a road through the pass in 1879 and converted it into a highway during the 1920s. A railroad was also built here in the 1920s.