Pythagoras in ~500 BC first suggested a spherical Earth based on philosophic grounds, Aristotle in ~350 BC provided the first empirical evidence to support the theory. He noted that Earth casts a circular shadow on the Moon during lunar eclipses, that ships disappear hull-first over the horizon, and that constellations shift depending on latitude. In ~240 BC, the mathematician Eratosthenes calculated the Earth's circumference with remarkable accuracy (within 1%) by measuring the difference in shadows in Alexandria and Syene on the summer solstice.