Refers to a defensive military structure, often a small fort or stronghold. Can also be used metaphorically for a stronghold or bastion of an idea or movement.
The ruins of an old fort remain on top of the mountain.
That area became the last stronghold of the rebel forces.
The soldiers built a fort on top of the mountain.
A small number of soldiers kept defending the fort until the end.
That hospital is called the last bastion of regional healthcare.
要塞 is a formal, heavily fortified military fortress, whereas 砦 can be a smaller fort and is also used more loosely, including metaphorically.
拠点 means a base or hub of operations with no military connotation, while 砦 keeps a fortress-like image even when used metaphorically for a stronghold of ideas.
Standard kanji form; common in news and modern writing.
Rarely used kanji form; may appear in historical or literary contexts.
Rarely used kanji form; may appear in historical or literary contexts.
The kanji 砦 is a kokuji (Japanese-created character) combining 石 (stone) and 此 (this), suggesting a stone structure. The reading とりで is of uncertain origin, possibly related to 取り出 (とりで) meaning 'take out' or 'defend'.