The Castle is a military/defensive building that, while expensive, is a worthwhile investment. It is a civilization’s most powerful fortification, able to garrison up to 20 units and to support 20 population (depending on civ). It is required to train most Unique Units, knightly units, and research a civilization's Unique Technologies. Guild Hall and Assembly Hall civilizations also use them to train Heroes. Castles fire a devastating number of arrows at any unit that gets in range. They require a lot of Stone, but if placed right they're worth it. The best counter for castles are siege weapons, such as rams, trebuchets or canon.
The Scottish, the Welsh and the Frisians have cheaper, but weaker Castles and can use them a bit more liberally for defense.
The English and The French have bigger Norman Castles, that are even stronger, but cost more stone.
The Teutonic Order can build exceptional castles, as they have an increased range and garrison, ranking them in between a standard castle and the big Norman Castles.
Castles fire four arrows with nobody garrisoned. Peasants and archers add extra arrows, with a maximum of twenty arrows fired on one volley. Ranged units add arrows at different rates, with archers being most effective, followed by cavalry archers, handgunners, javelineers, and peasants (roughly). Burgundy's Crenellations upgrade allows infantry to add arrows at the peasant rate.
(Key: Normal/Tower House/Norman)
Available to: All
Cost: 650/450/850 Stone
Armour/Pierce Armour: 8/8
Range: 8 (+1 in 15th century)
Garrison: 20/15/25 non-siege units.
Special: +2 vs. spearmen. 8 bonus armor vs. anti-building attacks. Supports 20/15/25 population.