The Mongolian unique unit. (Replaces Knight)
Quick - Regular - Epic - Marathon
Can move after attacking.
No defensive terrain bonuses; may not melee attack.
Great Generals I promotion
Gains 50% more XP from battles
The Keshik possesses a strong ranged attack and an increased movement rate (5 points total), allowing it to perform hit and run attacks remarkably effectively. Although its attack strength is a bit weaker than both the one of the standard knight and the Arabian Camel Archer, it has other advantages: it acquires more experience than the other units, and contributes twice the amount of points towards earning Great Generals. Also, Keshiks do not receive a penalty when attacking cities.
These mounted warriors singlehandedly afford Genghis Khan control of the open plains, by decimating enemy forces from afar and quickly advancing in levels and becoming more and more dangerous with each passing skirmish.
Stronger and faster than a crossbowman, about the only archery unit that can try to hold its own against a lot of Keshiks is the English longbowman, with its longer range. It is weaker, but has a range of 3 vs 2. You may try to use large numbers of longbowmen (if you are playing as England) to try and attack them. Using pikemen against Keshiks won't work very well, because Keshiks will just stand away from your pikemen and kill them one by one. Longswordsmen are too slow to attack Keshiks very well, despite their strength.
Another strategy is to use your own mounted units to rush the Keshiks before they can use their ranged attack. Keshiks are weaker than regular knights in melee combat, but they are also faster and can retaliate against your knights without taking damage themselves, so you will need to overwhelm them in as few turns as possible to avoid being worn down. If you are playing as Siam, Nareusan's Elephants are particularly devastating against Keshiks, because of their added strength and damage bonus against mounted units. Arabia's Camel Archers also have a ranged attack, so you can use the Keshiks' own tactics against them, provided you can catch them within attack range.
In the 13th century the Mongols came tumbling out of Central Asia, conquering most of Asia, Eastern Europe and a large portion of the Middle East by the end of the century. The Mongols' primary weapon was their incomparable horse archers, the Keshiks. The Mongols were nomadic tribesmen, and their children were almost literally "raised in the saddle." Riding on their small but hearty steppe ponies, the lightly-armed and armored Mongols could cover an astonishing amount of territory in a day, far outpacing any infantry or even the heavier European cavalry.
In battle the Mongol Keshiks would shoot from horseback with deadly accuracy, disrupting and demoralizing the enemy formations. Once the enemy was suitably weakened, the Mongol heavy cavalry units would charge into the wavering foe to deliver the coup de grace. When facing armored European knights the Mongols would simply shoot their horses, then ignore or destroy the unhorsed men as they wished.