Which Assassin's Creed game introduced the city of London as its main open-world setting?

Assassin's Creed Syndicate introduced London as its main open-world setting.

Released in 2015, Syndicate is set in London during the Industrial Revolution, around 1868. The playable Frye twins, Jacob and Evie, work to weaken Templar control and expand the influence of the Assassins across the city.

The game divides London into districts such as Westminster, the City of London, Whitechapel, and Southwark. Its mechanics reflect the period: players can use a rope launcher, travel by train, hijack carriages, and take part in gang activities. Historical figures including Queen Victoria and Charles Darwin appear in the campaign.

Unity is set in Paris, Rogue is set largely in the North Atlantic and North American colonies, and Revelations focuses on Constantinople. Syndicate is the series entry specifically built around Victorian London.