Definition: Eratosthenes was a Greek mathematician who devised a method to determine the height of buildings, trees, and other structures by measuring them from above. He is credited with being the first to use a compass to navigate on uneven ground. The term 'eratosthenes' refers to his method used for this purpose, which involved constructing a series of parallel lines to create a geometric figure resembling a pyramid. This technique was later adopted by other geographers and architects in subsequent centuries.