Keep

"Stronger than Watch Tower, with greater fighting ability."

- Age of Empires II description

The Keep is a Tower in Age of Empires II that becomes available once the Imperial Age is reached. Keeps are good against infantry and archers, but are not effective against siege weapons and most cavalry.

Tactics and Placement
Towers are an essential part of any kind of fortification. Keeps are very useful and valuable for defending the player's settlement against enemy raiding parties. Turtling strategies usually require the use of several Keeps among the use of Walls and Castles in order to create a strong fortification. Keeps should be placed in choke points to make them more effective or behind cliffs or forests. Keeps also work better if placed within the range of each other or within the range of a friendly Castle since both buildings will provide cover fire for each other. Also using Walls and Gates will protect them to some extent from Rams. In maps like Archipelago or Islands it is a wise idea to have several Keeps near the shoreline in order to take down potentially dangerous enemy fleets and give some support to the player's own fleet near the coast.

Offensively, Keeps can also be used for front line support as in a retreat they can hold troops that can be healed once garrisoned and they also provide cover fire for offensively placed military buildings if they are placed near an enemy location. In this regard they are better than a Castle since they are cheaper and are built quicker.

Keeps are highly vulnerable to long range siege units and Rams, so to protect them the player should have melee cavalry near to their fortifications, or some Fire Ships that can deal with the Cannon Galleons in case of Keeps placed near the shore.

Korean Keeps have 13 range, making them harder to deal with, because Bombard Cannons and Cannon Galleons cannot outrange them.

Garrisoned foot archers and Villagers increase the number of arrows Keeps fire, thus increasing the damage. Up to five (10 for the Teutons) foot-soldiers (infantry and archers, although infantry do not increase the firepower) may be garrisoned in a Keep. Garrisoned units slowly regenerate lost hit points.

If running for a Relic or Wonder victory, Keeps become a helpful tool to defend the Wonder or the Monasteries holding Relics, but the player will also require the support of several Castles, Walls, and other military structures. Also, the player must have sufficient numbers of troops (especially cavalry) for countering enemy siege units.

Civilization Bonuses

 * Burmese: Researching Faith and Herbal Medicine is 50% cheaper.
 * Byzantines: Keeps have +40% HP. Town Watch is free.
 * Chinese: Technologies that benefit Keeps are 20% cheaper.
 * Incas: Keeps cost 15% less stone.
 * Koreans: Keeps have +2 range and are built.
 * Malians: Keeps cost 15% less wood.
 * Spanish: Keeps are built 30% faster.
 * Teutons: Keeps can garrison up to 10 units. Murder Holes are free.

Team Bonuses

 * A team containing Ethiopians: Keeps have +3 Line of Sight.
 * A team containing Malians: University technologies that benefit Keeps are researched 80% faster.

The Age of Kings

 * Keeps have 7 attack.
 * Keeps have an attack bonus of +10 against camels because they share an armor class with ships.
 * The secondary arrows of Keeps deal 1 damage.

The Conquerors

 * Keeps gain an attack bonus of +2 against Spearmen.
 * Herbal Medicine introduced.
 * Heresy introduced.
 * Britons: Yeomen introduced.
 * Teutons: Crenellations introduced.

The Forgotten

 * Keeps now have 8 attack.
 * Celts: Stronghold introduced.
 * Incas: Cannot build Keeps.
 * Japanese: Yasama introduced. It gives Keeps three additional arrows.
 * Koreans: Keeps are now built 25% faster.

The African Kingdoms

 * Camels are moved out of the ship armor class, and Keeps lose their attack bonus against them. They now have +1 attack against them.
 * With patch 4.8, the secondary arrows of Keeps now deal 2 damage.
 * Arrowslits introduced. Initially, it gives Keeps +6 attack. With patch 4.8, Arrowslits now gives +3 attack.
 * Incas: Keep added to the technology tree.
 * Japanese: With patch 4.8, Yasama now gives Keeps two additional arrows.

History
''The central and strongest building inside a castle was called the keep. This was the last bastion of defense inside if the walls and outside towers were taken. The remaining defenders withdrew into the keep for the final defense. The keep was a mini-castle often constructed in place of a castle to cut expenses. Although much smaller than castles, keeps could perform the same function on a smaller scale. They were very difficult to capture except by a large and well-equipped army.''