A Bombard Tower and a Keep behind a wall in Age of Empires II: Definitive Edition.
Defensive structures are a type of building available in every game of the Age of Empires series. They are primarily used to defend their civilization from attacks, detect enemy armies, and garrison civilians, but can sometimes be used to train units or research technologies. Often, these defensive structures have an attack of their own, which helps them defend better, but some defensive structures allow only garrisoning. Walls (and gates) are a special class of defensive structures which neither attack nor garrison, but prevent or at least slow down the enemy army from reaching the protected area.
Generally speaking, there are three types of defensive structures: walls, towers, and Castle-type buildings.
In Age of Empires II, Age of Empires III, Age of Empires IV, and Age of Mythology, Town Centers get an attack of their own that can be improved by garrisoning Villagers or archers and double as defensive structures as a result, even though their primary function is economic.
Age of Empires[]
All defensive structures are researched and upgraded from the Granary:
Town Center (garrison only since Return of Rome)
Watch Tower → Sentry Tower → Guard Tower → Ballista Tower- Small Wall → Medium Wall → Fortified Wall
- Small Gate → Medium Gate → Fortified Gate
Towers found in campaigns and in the Scenario Editor:
Civilization bonuses[]
- Babylonians: Walls and towers have +60% hit points.
- Choson: All towers have +2 range.
- Romans: Towers cost -40%.
- Shang: All walls have +60% hit points.
Age of Empires II[]
Constructable[]
- Town Center
- Outpost (vision only)
- Watch Tower → Guard Tower → Keep
- Bombard Tower
- Palisade Wall
- Palisade Gate
- Stone Wall → Fortified Wall
- Gate → Fortified Gate
- Castle
- Harbor ( Malay only)
- House (garrison only, Khmer only)
- Krepost ( Bulgarians only)
- Donjon ( Sicilians only)
- Dock ( Gurjaras only)
- Fortified Church ( Armenians and Georgians only)
Unconstructable[]
The unconstructable defensive structures can only be found in campaigns and in the Scenario Editor:
Civilizations[]
Availability grid[]
| = Available | |
| = Unavailable | |
| = Researched for free or fully covered by a civilization bonus if unavailable |
| Civilization | 
|
|
|
|
|
|
|
|
|
|
|
|
|
Total |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 Armenians
|
10 | |||||||||||||
 Aztecs
|
8 | |||||||||||||
 Bengalis
|
11 | |||||||||||||
 Berbers
|
10 | |||||||||||||
 Bohemians
|
11 | |||||||||||||
 Britons
|
12 | |||||||||||||
 Bulgarians
|
8 | |||||||||||||
 Burgundians
|
12 | |||||||||||||
 Burmese
|
10 | |||||||||||||
 Byzantines
|
10 | |||||||||||||
 Celts
|
10 | |||||||||||||
 Chinese
|
11 | |||||||||||||
 Cumans
|
4 | |||||||||||||
 Dravidians
|
11 | |||||||||||||
 Ethiopians
|
9 | |||||||||||||
 Franks
|
8 | |||||||||||||
 Georgians
|
11 | |||||||||||||
 Goths
|
5 | |||||||||||||
 Gurjaras
|
11 | |||||||||||||
 Hindustanis
|
7 | |||||||||||||
 Huns
|
4 | |||||||||||||
 Inca
|
11 | |||||||||||||
 Italians
|
13 | |||||||||||||
 Japanese
|
10 | |||||||||||||
 Khmer
|
10 | |||||||||||||
 Koreans
|
12 | |||||||||||||
 Lithuanians
|
12 | |||||||||||||
 Magyars
|
8 | |||||||||||||
 Malay
|
9 | |||||||||||||
 Malians
|
10 | |||||||||||||
 Maya
|
11 | |||||||||||||
 Mongols
|
7 | |||||||||||||
 Persians
|
7 | |||||||||||||
 Poles
|
11 | |||||||||||||
 Portuguese
|
12 | |||||||||||||
 Romans
|
6 | |||||||||||||
 Saracens
|
10 | |||||||||||||
 Sicilians
|
|
6 | ||||||||||||
 Slavs
|
6 | |||||||||||||
 Spanish
|
11 | |||||||||||||
 Tatars
|
9 | |||||||||||||
 Teutons
|
10 | |||||||||||||
 Turks
|
13 | |||||||||||||
 Vietnamese
|
11 | |||||||||||||
 Vikings
|
11 | |||||||||||||
Civilization bonuses/Unique technologies[]
- Bohemians: Chemistry is available in the Castle Age.
- Britons:
- Bulgarians:
- Burmese: Researching Devotion, Faith, and Herbal Medicine are 50% cheaper.
- Byzantines:
- Defensive structures have +10%/+20%/+30%/+40% HP in the Dark/Feudal/Castle/Imperial Age.
- Town Watch and Town Patrol are free.
- Greek Fire: Bombard Towers have 0.5 blast radius that deals 25% damage.
- Celts: Stronghold: Castles and towers attack +25% faster.
- Chinese:
- Town Centers have +5 Line of Sight.
- Defensive technologies are 5%/10%/15% cheaper in the Feudal/Castle/Imperial Age.
- Great Wall: Walls and towers +30% hit points.
- Cumans: Can build a second Town Center in the Feudal Age.
- Franks: Castles are 15%/25% cheaper in the Castle/Imperial Age.
- Georgians:
- Defensive structures receive -20% damage (-40% instead of -25%) when fighting from higher elevation.
- Svan Towers: Defensive Structures +2 attack; Towers fire arrows that pierce multiple targets.
- Gurjaras: Can garrison Docks with allied Fishing Ships.
- Inca: Defensive structures cost -15% stone.
- Italians: University technologies which benefit defensive structures are 33% cheaper.
- Japanese: Yasama: Towers fire +2 arrows.
- Khmer: Can garrison Houses with allied Villagers.
- Koreans:
- Tower upgrades are free (Bombard Towers require Chemistry).
- Eupseong: +2 Watch Tower line range.
- Malay: Thalassocracy: Upgrades their Docks to defensive structures (Harbors).
- Malians:
- Persians:
- Portuguese:
- Technologies which benefit defensive structures are researched 25% faster.
- Arquebus: Increases projectile speed of Bombard Towers by 0.2.
- Romans: Defensive structures are built and repaired 5% faster.
- Sicilians:
- Town Centers are constructed 100% faster, Fortifications are built 50% faster.
- Can build Donjons (instead of Watch Towers).
- Spanish:
- Defensive structures are built 30% faster.
- Fletching, Bodkin Arrow, and Bracer don't cost gold.
- Researching technologies which benefit defensive structures provides 20 gold.
- Teutons:
- Towers can garrison twice as many units and can fire +4 arrows.
- Town Centers can garrison +10 units and can fire +5 arrows.
- Murder Holes is free.
- Crenellations: Castles +3 range; Garrisoned infantry fire arrows
- Turks:
- Chemistry is free and the Bombard Tower technology is 50% cheaper.
- Artillery: Bombard Towers +2 range
Team bonuses[]
- Bulgarians: Fletching, Bodkin Arrow, and Bracer are researched 80% faster.
- Cumans: Palisade Walls (and Gates) have +33% hit points.
- Ethiopians: Outposts have +3 Line of Sight, cost no stone.
- Georgians: Defensive Structures cost 25% fewer resources to repair.
- Lithuanians: Devotion, Faith, Herbal Medicine, and Heresy are researched 20% faster.
- Malians: University technologies are researched 80% faster.
- Maya: Walls (and Gates) are 50% cheaper.
- Portuguese: Defensive technologies are researched 25% faster.
- Teutons: Towers are more resistant to conversion.
- Vikings: Harbors (Malay only) and Docks (Gurjaras only) cost -15% wood.
Age of Mythology[]
All defensive structures (except for fully upgraded walls) can research technologies that upgrade themselves. Towers can also research technologies that improve building Line of Sight.
- Town Center
- Sentry Tower
- Watch Tower (Egyptians only free automatically upgrade Classical Age)
- Guard Tower (except Norse Heroic Age)
- Ballista Tower (Egyptians only Mythic Age)
- Wooden Wall
- Earthen Wall (Chinese only Archaic Age)
- Stone Wall (Classical Age)
- Fortified Wall (except Norse Heroic Age)
- Citadel Wall (Egyptians only Mythic Age)
- Great Wall (Chinese only Mythic Age)
- Bronze Wall (Atlantean Classical Age)
- Iron Wall (Atlantean Heroic Age)
- Orichalcum Wall (Atlantean Mythic Age)
- Mirror Tower (Atlantean only available through the worship of Helios, except Gaia)
Age of Empires III[]
- Town Center
- Dock (only against ships when garrisoned by Fishing Boats)
- Outpost (European civilizations only, except Russians)
- Blockhouse (Russians only, Indian campaign and Chinese with Russian Consulate ally)
- War Hut (Native American civilizations only)
- Castle (Asian civilizations only)
- Trading Post (with the "Advanced Trading Post" Home City Card)
- Tambo (Inca only)
- Wall
- Gate
- Teepee (Lakota only, substitution for the absence of Walls until the Industrial Age. Cannot attack, but boosts combat ability of nearby units)
- Nobles' Hut (Aztecs only)
- Kallanka (Inca only)
- Fort (European civilizations only, with Home City Card, Indian campaign and Chinese with Russian Consulate ally)
- Agra Fort (Indian Wonder)
- Stronghold (Inca only)
- Fixed Gun (Campaign and Scenario Editor only)
- Tower (Campaign and Scenario Editor only)
- Fixed Gun (Maltese only)
- Commandery (Maltese only)
- American Citadel
Age of Empires IV[]
- Town Center
- Dock (once naval arrowslits are added)
- Outpost
- Palisade Gate
- Palisade Wall
- Stone Wall
- Stone Wall Gate
- Stone Wall Tower
- Keep
- Castle (Japanese only)
- Wooden Fortress (Rus only)
- Fortified Palisade Gate (Rus only)
- Fortified Palisade Wall (Rus only)
- Barbican of the Sun (Chinese Landmark)
- Imperial Palace (Chinese Landmark)
- Great Wall Gatehouse (Chinese Landmark)
- The White Tower (English Landmark)
- Berkshire Palace (English Landmark)
- Red Palace (French and Jeanne d'Arc Landmark)
- Elzbach Palace (Holy Roman Empire and Order of the Dragon Landmark)
- Saharan Trade Network (Malian Landmark)
- Fort of the Huntress (Malian Landmark)
- Kremlin (Rus Landmark)
- Spasskaya Tower (Rus Landmark)
- Castle of the Crow (Japanese Landmark)
