noun
fort; defensive position
Refers to a fortified military position or stronghold. Somewhat formal or technical; in everyday speech, 要塞 (ようさい) is more common.
敵は川沿いに防塞を築いた。
The enemy built a fort along the river.
この地域には古い防塞の跡が残っている。
Remains of old defensive positions remain in this area.
要塞 is the common word for 'fortress' or 'stronghold' in modern Japanese. 防塞 is more technical and less frequent.
Compound of 防 (defend) and 塞 (fortress/block). The exact historical derivation is uncertain, but the word follows standard Sino-Japanese word formation.