Even 6000 years ago, horsemen recognized the need for a bit. Originally as a way to control the horse. Archaeological evidence of the first domesticated horse populations, indicate that their riders used twisted rawhide for mouthpieces with carved antlers for cheek pieces. The Iron Age brought metal bits but they basically remained the same as they are still these days.
The bit is a relatively simple piece of equipment, surrounded by many complex theories and certainly some misperceptions.
Today, as the relationship between man and horse has developed to primarily recreational sport, the bit has become an important tool of communication.