Thales was a geometer, military engineer, astronomer, and logician. Probably influenced by Babylonians and Egyptians, Thales discovered the solstice and equinox and is credited with predicting a battle-stopping eclipse thought to be on 8 May 585 B.C. (the Battle of Halys between Medes and Lydians). He invented abstract geometry, including the notion that a circle is bisected by its diameter and that the base angles of isosceles triangles are equal.