Cuneiform, the world's oldest known writing system, was developed by the ancient Sumerians of Mesopotamia around 3400-3100 BC. It was written by pressing a stylus into wet clay tablets, leaving wedge-shaped marks. Cuneiform was used for over 3,000 years and was eventually deciphered by 19th century scholars, unlocking a vast library of ancient texts on trade, law, and literature.