Combining the functions of the European Outpost and Artillery Foundry, the Castle possesses defensive capabilities like the RussianBlockhouse and Native American War Hut. It starts as an Flatland Castle and can be upgraded to a Hill Castle in the Fortress Age, then a Mountain Castle in the next. Without Home City cards, only five Castles can be built.
"The fortification of towns had been in practice since ancient times, exhibited in the high-walled cities of Rome and the palaces of Byzantium; but in the ninth century, the feudal lords of Europe began to experiment with the castle, or fortified residence. These began as an elevated patch of terrain surrounded by a primitive ditch. Throughout medieval times, as siege technology developed and the threat of war constantly loomed, European rulers began to raise the walls of their fortresses higher and higher, and thicker walls were topped with towers and parapets.
By the thirteenth century, castles had become highly sophisticated, and the integral spine to any kingdom. First, a strategic location was chosen, such as on a high cliff or at the bend in a river. Then a moat was dug, restricting access to a narrow point that was often blocked by a retractable drawbridge. The keep, or innermost part of the castle, was protected by a series of walls that had to be breached in order to enter, defeat the survivors, and claim victory.
The earliest Japanese castle was the yamashiro, a deforested hill carved into a series of walls and courtyards. Each of the horizontal baileys gave defenders an open view of the battlefield. Because it had the same primarily defensive purpose as the European castle, the yamashiro shared many of the same features, with its squat, angular walls surrounding ditches. Also, both structures housed barracks and training facilities for a standing army led by the elite warrior class (the samurai, in the case of the Japanese)."