the ideas of anaximander (c. 610–545 bc): considered by later greek writers to be the true founder of geography, come to us through fragments quoted by his successors. anaximander is credited with the invention of the gnomon, the simple, yet efficient greek instrument that allowed the early measurement of latitude. thales is also credited with the prediction of eclipses. the foundations of geography can be traced to the ancient cultures, such as the ancient, medieval, and early modern chinese. the greeks, who were the first to explore geography as both art and science, achieved this through cartography, philosophy, and literature, or through mathematics. there is some debate about who was the first person to assert that the earth is spherical in shape, with the credit going either to parmenides or pythagoras. anaxagoras was able to demonstrate that the profile of the earth was circular by explaining eclipses. however, he still believed that the earth was a flat disk, as did many of his contemporaries. one of the first estimates of the radius of the earth was made by eratosthenes.