"Let other people play other things – the king of game is still the game of kings" – stone inscription in a polo playground in Gilgit, north of Kashmir, near the famous silk road from China to the West.

The precise source of polo is ambiguous, however, many scholars agree that polo originated among the Iranian tribes before the rule of Darius (521-485 BC) whose cavalry created the second Iranian Empire, the Achaemenid dynasty. Indeed, Persians gave us the richest accounts in art and literature documenting polo.

Ferdowsi, a well known Iranian poet and historian, wrote about royal polo tournaments in his 9th century epic Shahnameh (Epic of Kings). The poet is moving in his praise of Siyawash's skill on the playfield. Additionally, Ferdowsi speaks of Emperor Sapour II of the 4th century Sasanian dynasty, who learned to play polo when he was seven years old.

Dinvary, another 9th century historian, wrote about polo, its rules and general guidelines. Among his advice is exercising a lot and if a stick breaks then it's a sign of inefficiency. Players should avoid strong language and be calm and patient. In the 10th century King Qabus of Persian Ziyarid dynasty similarly wrote about rules and mentioned the risks of the game.

Omar Khayyam referred to polo to illustrate philosophical points. Nezami (1126-1180), another poet, wrote a love story about Khosrow (590CE) and his consort Shirin, and her ability to play polo in the field. A description mentions Khosrow's all male team against Shirin's all female team.

Polo is a team game played on a field with one goal for each team. Each team has three or four players. Polo features successive periods called chukkas, and riders score by driving a ball into the opposing team's goal using a long-handled mallet. In this it is similar to many team sports such as football and field hockey. The main difference is that the players play on horseback.

When playing outdoors each team has four players, while arena polo is restricted to three players per team. The field is 300 yards long, and either 160 yards or 200 yards wide. There is a goal on either end of the field. The object of the game is to score the most goals by hitting the ball through the goal.

Game is divided into periods, called chukkas, of 7 minutes, and depending on the rules of the particular tournament or league, a game may have 4, 6 or 8 chukkas. Games are often played with a handicap in which the sum of the individual players' handicaps are compared to each other, and the team with the worse handicap is given a few goals before the start of the game.

References:

http://en.wikipedia.org/wiki/Polo
http://www.cais-soas.com/CAIS/Sport/polo.htm
http://members.tripod.com/~TheManipurPage/history/polo.html