In 530 BC Cyrus the Great, King of the Persian Achaemenid Empire crossed the Hindu-Kush mountains to seek tribute from the tribes of Kamboja, Gandhara and the trans-India region (modern Afghanistan and Pakistan). By 520 BC, during the reign of Darius I of Persia, much of the northwestern subcontinent (present-day eastern Afghanistan and Pakistan) came under the rule of the Persian Achaemenid Empire, as part of the far easternmost territories. The area remained under Persian control for <answer>two centuries</answer>. During this time India supplied mercenaries to the Persian army then fighting in Greece.
How long did the Persian empire control the northern India subcontinent?
two centuries