Bulwark is a general word for any defensive wall or rampart; its only technical use at present is in nautical language, where it signifies the raised side of a ship above the upper deck, topped by the rail.

J. C. Fernald, English Synonyms and Antonyms (1914)

Example sentences

fortress The fortress was secure from every kind of attack.
stronghold The last stronghold of humanity has finally fallen.
rampart I'll answer any question, as long as it pertains to Rampart.
breakwater The breakwater had no effect against the tsunami.

Popularity over time

Word	1850 → 2019	Trend
bulwark		steady
fortress		rising
stronghold		rising
bastion		steady
rampart		steady

Use in printed books, per decade from 1850 to 2019.

By length

4 letters: wall¹, fort¹, mole¹
5 letters: guard¹, mound¹, groin¹, jetty²
6 letters: shield¹, groyne
7 letters: defense², defence², barrier³, bastion², citadel³, rampart², parapet³, redoubt²
8 letters: fortress²
9 letters: palladium⁴
10 letters: protection³, stronghold², breakwater³
12 letters: entrenchment³
13 letters: fortification⁵

The small number after each word is its number of syllables (jetty² = 2 syllables).

In other languages

Français: bastingage
Deutsch: Reling