堡

A phono-semantic compound consists of:

土 (earth; soil) — semantic component, indicates earthworks or land structures.

保 (to protect) — phonetic component, supplies pronunciation "bo" and reinforces the idea of protection.

Thus the original meaning suggests "an earthen structure built for protection."

Semantic development:

- earthen fortification;

- defensive stronghold;

- small walled settlement;

- embankment or dike (by extension).

보루 (堡壘) — fortress; stronghold

성보 (城堡) — castle

방죽 / 둑 — embankment (extended meaning)

堡 emphasizes relatively small, protective fortification, often constructed from earth.

Related сharacters:

城 — city wall

壘 — fortress

塞 — frontier pass

堤 — dike

防 — defend

Among these, 堡 most clearly denotes a small fortified defensive earth structure.

Metaphorical usage:

思想堡垒 — ideological stronghold

Classical / historical usage:

築堡守邊 — “Build forts to guard the frontier”

邊堡 — border fort