Frontier fortification is a tag in Age of Empires III: Definitive Edition, referred to as AbstractOutpost in the game files. Frontier fortification are Outpost-type buildings; in other words, they are defensive buildings which attack nearby enemy units, are effective against weaker enemies, and reveal stealth enemies. They are vulnerable to artillery and siege units.
The following buildings are labeled as Frontier fortification:
Outpost
Blockhouse
War Hut
Nobles' Hut- Castle
- Regent's Castle
- Tower
- Watch Tower
- Palace
- Battery Tower
- Fixed Gun
- Commandery
The following buildings are not labeled as Frontier fortification:
Technologies[]
The technologies and upgrades that affect buildings with the Frontier fortification tag are shown below:
- Somali Ajuran Engineers (+4 build limit)
- Sentry Tower and Guard Tower (+5 Line of Sight)
| Tags in Age of Empires III | |
|---|---|
 Infantry | |
 Heavy infantry | Hand infantry ·  Pikeman · Musket infantry |
 Light infantry | Foot archer · Rifle infantry · Hand skirmisher |
| Other | Counter skirmisher · Gunpowder trooper · Grenade trooper |
 Cavalry /  Shock infantry | |
 Heavy cavalry |  Hand cavalry · Ranged heavy cavalry · Lance cavalry |
 Light ranged cavalry | Gunpowder cavalry |
| Shock infantry |  Hand shock infantry ·  Ranged shock infantry |
| Other | Camel · Elephant |
| Siege units | |
 Siege trooper ·  Artillery ·  Siege Elephant · Gatling Camel* · Fixed Gun* · Arrow Knight* | |
 Ships | |
Fishing boat · War ship ·  Recruiting ship | |
 Building | |
 Resource enclosure ·  Wall · Frontier fortification · Barracks | |
| Other | |
 Hero ·  Mercenary · Monk ·  Outlaw ·  Pet ·  Villager | |
| Mother nature | |
 Hunted animals ·  Treasure guardian | |
| Support tags | |
| Archer · Healing unit · Native warrior · Archaic infantry · Ranged infantry · Ranged cavalry · Consulate unit | |
| All tags with icons are related to the bonus and penalties counter system, except *hidden tags that aren't in the UI | |