The Pythagorean Society was an ancient philosophical and religious group founded by the Greek mathematician Pythagoras around the 6th century BCE. This society focused on the study of mathematics, particularly geometry, and believed that numbers were the essence of all things. Members followed strict rules, including communal living and dietary restrictions, and engaged in various intellectual pursuits. The society's teachings emphasized the importance of harmony and order in the universe, which they believed could be understood through mathematics. They contributed significantly to the development of mathematical concepts, including the famous Pythagorean theorem, which relates the sides of a right triangle.