The most important areas of Greek achievement were math and science. They achieved all kinds of things in the areas of psychology, astronomy, geometry, biology, physics, and medicine. In astronomy they formulated the ideas that the sun was 300 times larger than the earth, the universe was composed of atoms, and they calculated the true size of the earth. Someone greatly involved in astronomy was Aristotle. In geometry, ancient Greeks found the value of pi, and a man named Euclid, who wrote the book Elements around 300 ., theorized that if two straight lines cut one another, the vertical, or opposite, angles shall be equal. In physics, the lever and pulley was invented along with a force pump which eventually evolved into a steam engine. Important people in this area were Archimedes and Pythagoras who were two of the many influential Greek citizens. Ancient Greece has definitely made many influential contributions to western civilization.