Thales and Pythagoras

From around 600 BC until the 5th century AD, mathematics and astronomy flourished in parts of the Greek-speaking world of the eastern Mediterranean Sea. During this time, the Greeks developed the concept of deductive logical reasoning that became the hallmark of much of their work, especially in the area of geometry.
The earliest known Greek mathematician is Thales of Miletus (c.624–547 BC) who, according to legend, brought geometry to Greece from Egypt. He predicted a solar eclipse in 585 BC and showed how rubbing with a stone can produce electricity in feathers. In geometry he investigated the congruence of triangles, applying it to navigation at sea, and is credited with proving that a circle is bisected by any diameter and that the base angles of an isosceles triangle are equal.
The semi-legendary figure of Pythagoras (c.572–497 BC) was born on the Aegean island of Samos, later emigrating to the Greek seaport of Crotona (now in Italy) where he founded a brotherhood, the Pythagorean school. According to later writers, this closely-knit group was formed to further the study of mathematics, philosophy and the natural sciences. The Pythagoreans supposedly believed that ‘All is number’, and there was a particular emphasis on the ‘mathematical arts’ of arithmetic, geometry, astronomy and music. Pythagoras is one of the Greek scholars depicted in Raphael’s Vatican fresco The School of Athens.
[Greece 1955, 1994; San Marino 1983; Sierra Leone 1983]