Eudoxus of Cnidus was a Greek mathematician, astronomer, and geographer active in the 4th century BCE. He was born in the city of Cnidus in Asia Minor. He studied with the Pythagorean Archytas in Italy and later attended lectures at Plato’s Academy in Athens. He also traveled to Egypt for further study before returning to Cnidus, where he established an observatory and served as a lawgiver.

Although none of his own writings survive, his ideas are preserved through later ancient authors. His major contributions were in astronomy and mathematics. In astronomy, he proposed a model of concentric spheres to explain the complex motions of the planets, which became highly influential. He also wrote descriptive works on constellations and geography. In mathematics, he developed a rigorous theory of proportion and a method for calculating areas and volumes known as the method of exhaustion. According to modern scholars, these mathematical tools were essential for the later work of Euclid and Archimedes.

Eudoxus is considered a pivotal figure in the history of science. His geometric model of the heavens was the dominant astronomical theory for centuries, and his mathematical innovations provided a foundation for Greek geometry. Despite the loss of his original treatises, his legacy is deeply embedded in the scientific tradition of antiquity.