The high altitudes of the mountains have historical significance in South and Central Asia. The Hindu Kush range was a major centre of Buddhism with sites such as the Bamiyan Buddhas. It has also been the passageway during the invasions of the Indian subcontinent, a region where the Taliban and Al Qaeda grew, and to modern era warfare in Afghanistan. In ancient mines producing lapis lazuli are found in Kowkcheh Valley, while gem-grade emeralds are found north of Kabul in the valley of the Panjsher River and some of its tributaries. According to Walter Schumann, the West Hindu Kush mountains have been the source of finest Lapis lazuli for thousands of years.