Polymath, geographer and early comparative scholar of religion
Born in Khwarezm, he measured the Earth's radius from a mountaintop, learned Sanskrit to study India on its own terms, and wrote about Hindu belief without condescension.
Key achievements
Estimated the Earth's radius to within a fraction of a percent of the modern figure
Wrote Tarikh al-Hind, a study of Indian science, religion and custom
Argued that the Earth rotates on its own axis, centuries before it was accepted