The name India is derived from the river Indus. The game of chess originated from India. The decimal code along with the place value system was an original Indian development. The highest cricket ground of the world is in Chail, approximately 2444 meters above sea level. Budhayana an Indian mathematician was the first to calculate the value of "pi" mathematically and explained the concept of Pythagorean Theorem in the 6th century. The Indian railway is the largest employer in the world, over a million people work for it. The game of snake and ladders was discovered in India by Gyandev in the 13th century.