Though there is controversy over the exact date horses were domesticated and when they were first ridden, the best estimate is that horses first were ridden approximately 4,500 BC. Indirect evidence suggests that horses were ridden long before they were driven. There is some evidence that about 6000 years ago, people were using bits on horses. However, the most unequivocal early archaeological evidence of equines put to working use was of horses being driven. Chariot burials about 2,500 BC present the most direct hard evidence of horses used as working animals. In ancient times chariot warfare was followed by the use of war horses as light and heavy cavalry.