The city building sim CityVille, has deposed FarmVille as the biggest game ever on Facebook, just a month after its release. CityVille's active monthly audience reached 84.2 million users, an improvement of 400,000 on FarmVille's total of 83.8 million.

Zynga credits this remarkable growth to three factors. Firstly, it's the first Zynga game to have a multi-lingual release. Secondly, the game has received a lot of word of mouth advertising, and finally, Zynga has made extensive use of cross-promotion, and advertised it in other games like Mafia Wars and FrontierVille.

This success doesn't come as a complete surprise, as there were signs that the game was going to be a hit, even from day one. CityVIlle saw the most successful launch of any Zynga game to date, more than twice what FrontierVille managed on its first day. CityVille is currently growing by around two million users a day, and it's thought that it's active user base will eventually exceed 100 million users.

                                                                                       Source: Escapist Magazine