monumento

The tail of this word is a trap for anyone who has started noticing suffixes. -Ment- is a live suffix in English, French and Spanish, so monu-ment-o looks decomposable. It is not: Esperanto has no -ment- suffix at all, and monument- is one root borrowed whole. Where English uses -ment to make a noun from a verb, Esperanto uses -ado for the action and -aĵo for the thing, so "movement" is movado and "monument" is just monumento.

The word covers more than statues. A monumento is anything raised or preserved to keep a memory: a war memorial, a standing stone, a protected building, and by extension a great work. La Fundamento estas monumento de la lingvo is a normal sentence in Esperanto writing, and it means what the English cognate would mean. The adjective monumenta reaches the same figurative sense, so a monumenta verko is a monumental work.

Beside it, statuo is narrower and more concrete: a statue is a figure of a person or animal, whether or not it commemorates anything. Every statue on a plinth in a square is a statuo; only the ones put there to be remembered by are also monumentoj.