early 13c., "mental weakness; foolish behavior or character; unwise conduct" (in Middle English including wickedness, lewdness, madness), from Old French folie "folly, madness, stupidity" (12c.), from fol (see fool (n.)). From c. 1300 as "an example of foolishness;" sense of "costly structure considered to have shown folly in the builder" is attested from 1650s. But used much earlier, since Middle English, in place names, especially country estates, probably as a form of Old French folie in its meaning "delight." Related: Follies.
1754 in reference to peculiar behavior, 1794 of a fantastic type of performance or writing, from Italian extravaganza, literally "an extravagance," from estravagante, from Medieval Latin extravagantem (see extravagant). Related: Extravaganzist.
<a href="https://www.etymonline.com/word/follies">Etymology of follies by etymonline</a>
Harper, D. (n.d.). Etymology of follies. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/follies