Game Info:
City must have a Castle or Mughal Fort.
Strategy:
The Arsenal is a Renaissance-era military building that increases a city's Defensive Strength. The city must possess a Castle or Mughal before it can construct an Arsenal.
Historical Info:
An arsenal is a larger and more extensive armory, containing an army's bigger and more dangerous weapons systems - tanks, artillery, high-explosive ammunition, and so forth. Arsenals are even more heavily-guarded than armories, since nobody wants anybody stealing a tank or an 88-mm explosive shell.