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 soldiers built a fort on top of the mountain.
The ruins of an old fort remain on top of the mountain.
That area became the last stronghold of the rebel forces.
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'.