"Là, une multitude d'étals de poissons fraîchement pêchés aiguisaient l'appétit des passants"
I don't understand the plural here: Isn't it "Une multitude d'étals" - multitude being singular - which is the subject of the verb - rather than "D'étals" themselves, which would be plural.
I'm trying to devine whether there is some rule at work here here, or whether it's pretty much optional.