fort; stronghold; fortification
Refers to a fortified military structure or defensive position. Used in both historical and modern contexts.
They built a fortress on top of the mountain.
This old castle was once an impregnable fortress.
The enemy built a fort on top of the mountain.
The enemy forces attacked the fortress.
After a long siege, the fortress fell.
There is a plan to turn this island into a fortress.
陣地 is a military position or encampment set up for battle, whereas 要塞 is a fixed, heavily fortified structure.
要塞 is the standard modern word for a fortress, whereas 塁 is a more literary term often referring specifically to an earthen rampart or defensive works.
要塞 emphasizes a modern military fortress or stronghold, whereas 城郭 typically denotes a traditional Japanese castle and its surrounding walls.
要塞 is the broad term for any fortress or stronghold, whereas 台場 refers specifically to a coastal artillery battery, especially from the Edo period.
要塞 means a fortified military installation (a fortress), while 要衝 refers to a strategically important location that need not be fortified at all.
Sino-Japanese compound: 要 (key point, important) + 塞 (block, fortify). The combination conveys a strategically important fortified place.