[Source:] Loss of Latin -v- is regular in French in some situations (compare alleger from alleviare; neige from nivea; jeune from juvenis. A different sound evolution from the Latin word yielded Italian citta, Catalan ciutat, Spanish ciudad, Portuguese cidade.
Why might the Latin -v- have been lost in French? The following discusses the influence of the Gaulish language on French. So did Gaulish cause this loss?
[Source:] One example of a substrate language is Gaulish, from the ancient Celtic people The Gauls. The Gauls lived in the modern French-speaking territory before the arrival of the Romans namely, the invasion of Julius Caesar's militia. Given the cultural, economic and political advantages that came with being a Latin speaker, the Gauls eventually abandoned their language in favor of the language brought to them by the Romans, which evolved in this region until eventually it took the form of the French language that is known today. The Gaulish speech disappeared, but remnants of its vocabulary survive in some French words (approximately 150) as well as place-names of Gaulish origin. [...] In the case of French, for example, Latin is the superstrate and Gaulish the substrate.