Guard Tower (Age of Empires II)

In Age of Empires II, the Guard Tower is third available tower (after the Outpost and Watch Towers), first available on the Castle Age to all civilizations except Goths and Huns. They are the upgrade of the Watch Tower, researched from the University. Like the Watch Tower, Guard Towers are very good against infantry and archers, but are quickly overpowered by siege weapons like the Battering Rams and large groups of Cavalry. Guard Towers can be upgraded to a Keep for and  at the University once Imperial Age is reached.

Tactics and Placement
Towers are an essential part of any kind of fortification. The Guard tower like its predecessor the Watch tower are very useful and valuable for defending the player's settlement against enemy raiding parties. Turtling strategy will require the use of several Guard towers among the use of walls and Castles in order to create a strong fortification. Guard towers must be placed in choke points to make them more effective or behind cliffs or forests, Guard towers 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 Archipielago and Islands it is a wise idea to have several Guard towers near the shore line in order to take down potentially dangerous enemy fleets and give some support to the player's own fleet near the coast.

Offensively Guard towers can also be used for front line support as in a retreat they can hold troops that can be healed once inside them and it also provides cover fire for buildings like Barracks, Stables, Archery Ranges and Siege Workshops if they are placed near an opponent location, in this regard they are better than a Castle since they are cheaper and are created quicker.

Guard Towers however are highly vulnerable to long range siege units (Trebuchet, Bombard Cannon and Cannon Galleon) and Rams, so to protect them in most cases the player must have melee cavalry near to their fortifications, or if it is a Guard tower in the coast line the player must have some Fire Ships that can deal with the Cannon Galleons. Garrisoned foot archers and Villager will increase the number of arrows the tower fires, thus increasing the damage. Up to five foot-soldiers (infantry and archers, although infantry do not increase the firepower of the tower) may be garrisoned into the Guard tower (Teutons are an exception to this rule). When garrisoned in the Guard tower (or any other building) units will slowly regain any lost hit points.

Civilization Bonuses

 * Byzantines: Guard Towers have 30%/40% more Hit Points in Castle/Imperial age. Town Watch upgrade is free.
 * Chinese: Technologies that benefits Guard Towers are 10%/15%/20% cheaper in Feudal/Castle/Imperial age.
 * Teutons: Guard Towers can garrison at most 10 Archers or Infantry units at one time. This also doubles the maximum number of arrows that can be fired.
 * Spanish: Guard Towers are built 30% faster.
 * Koreans: Guard Towers have additional range by one point from Castle Age beyond. In addition, Korean towers upgrades itself to Keeps automatically in the Imperial Age.
 * Incas: 15% stone discount on buildings applies to Guard Towers.
 * Malians: Guard Towers costs 15% less wood.

Team Bonuses
A team Containing Ethiopians: Guard Towers have +3 LOS.

Changes in The Forgotten Expansion

 * Guard Towers have +1 Attack.
 * Koreans: Build Guard Towers and other defensive structures 25% faster among its other bonuses.
 * Britons: Yeomen technology moved to Castle age, adds +2 attack to Guard Towers.
 * Celts: Stronghold technology increases the rate of fire of the tower by 20%.
 * Japanese: Yasama technology makes their towers fire 3 extra arrows (4 in total, ungarrisoned).

Changes in The African Kingdoms Expansion

 * Arrowslits introduced.

History
"The defensive tower continued to evolve during the Middle Ages by getting stronger, taller, and better designed for fighting defense. Whereas some earlier watch towers had been square, guard towers were usually round to eliminate a sharp corner that could be knocked off. Fighting positions at the top of a guard tower were improved to protect defenders. Hoardings extended out from the top, allowing defenders to reach the bottom of the guard tower with missiles. Entrances to guard towers were made more elaborate and more easily defendable."

- Age of Empires II manual