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Walls are replaced by the following unique building:
Strategy[]
Walls increase a city's defenses against pre-gunpowder units. Build them in cities under threat from enemy or barbarian assault.
Civilopedia entry[]
Before the establishment of centralized governments capable of supporting strong, national armies, individual cities were left to fend for themselves when it came to defense. As a result, many cities constructed city walls to protect against raiders and bandits. City walls represented a major investment in both time and materials, requiring years to complete and constant repairs to maintain their strength and integrity. However, these walls turned the city into a fortress capable of withstanding all but the most determined attack. The development of gunpowder largely put an end to the usefulness of walls in stopping large armies.
