Polo is the oldest team sport in known history, with the first polo matches being played in Persia over 2500 years ago. Polo was first a training game for cavalry units, usually the king's guard or elite troops. As mounted armies swept back and fourth, conquering and re-conquering, polo was adopted as the most noble of pastimes by Kings and Emperors, Shahs and Sultans, Khans and Caliphs of the ancient Persians, Arabs, Mongols and Chinese. It was for this reason it became known as "the game of kings".