In which city is most of Assassin's Creed Unity set?

Most of Assassin's Creed Unity is set in Paris.

Released in 2014, Unity follows Arno Dorian, an Assassin operating during the French Revolution. Its detailed open-world recreation includes landmarks, streets, interiors, and districts across Paris, making the city the game's defining setting.

The story begins before the Revolution and continues through major years of political upheaval. Arno becomes involved with the Assassin Brotherhood while investigating the death of his adoptive father and the activities of Templar factions.

The game also includes locations outside central Paris, including Versailles. It is therefore more precise to say that Paris is the primary setting rather than the only location. London is the main setting of Assassin's Creed Syndicate, while Rome dominates Brotherhood and Florence is especially important in Assassin's Creed II.