Kabul is located high up in a narrow valley between the Hindu Kush mountains and bounded by the Kabul River, with an elevation of  making it one of the highest capitals in the world. The city is said to be over 3,500 years old, mentioned since at least the time of the Achaemenid Empire. Located at crossroads in Asia – roughly halfway between Istanbul in the west and Hanoi in the east – it is in a strategic location along the trade routes of South and Central Asia, and a key location of the ancient Silk Road. It has been part of the Achaemenids followed by the Seleucids, Mauryans, Kushans, the Sasanians (Kushano-Sasanians), the Hindu Shahi and Turk Shahis, Saffarids, Samanids, Ghaznavids, Ghurids, Khwarazmians, Qarlughids, Khaljis, Timurids, Mughals, and Hotaks, until finally becoming part of the Afghan Durrani Empire in 1747. Kabul became the capital of Afghanistan in 1776 during the reign of Timur Shah Durrani, the son of Ahmad Shah Durrani. In the early 19th century, the British occupied the city, but after establishing foreign relations, they were compelled to withdraw all forces from Afghanistan.