Archytas

Archytas lived in Taras, the Greek city in what's now southern Italy, sometime between 435 and 350 BC. He was a mathematician, music theorist, and statesman who moved in Pythagorean circles and counted Plato as a friend. Where other Greek thinkers leaned on geometry, Archytas insisted that arithmetic gave the only satisfactory foundation for proof - a position that set him apart. He's credited as the founder of mathematical mechanics, and in antiquity his argument for the infinity of the universe became the most widely known defense of the idea. He also served as a strategist, folding philosophy into the practical business of running a city.