In 1017 A.D., Sultan Mahmud, ruler of a great empire in what is now Afghanistan and Iran, brought to his court at Ghazna many of the most brilliant scholars of the Islamic world. Among them was Alberuni (or Al Biruni), who was renowned as a mathematician, astronomer, and political philosopher. Alberuni's aim was to acquire an exact understanding of the Hindus' knowledge of the natural world, to make it possible for Muslims "to converse with the Hindus, and to discuss with them questions of religion, science, or literature, on the very basis of their own civilization." For thirteen years he traveled in North India, observing, questioning, and studying. The result was an account of Indian culture that is unique in its sympathetic understanding, shrewdness of observation, and probing analysis.