997 – Versus de scachis is the earliest known work mentioning chess in Christian Western Europe.[2] 1008 – Mention of chess in the will of Count Uregel, another early reference. 10th century – As-Suli writes Kitab Ash-Shatranj, the earliest known work to take a scientific approach to chess strategy. late 10th century – Dark and light squares are introduced on a chessboard.