Sid Meier’s Civilization has had a very strong 25 years since the first game launched in 1991, selling 33 million units across the entire series. This was revealed by Meier at the DICE Summit 2016 during a panel focused on the 25th anniversary of the franchise.

As per VentureBeat, Meier said that with regards to the first Civilization, “There was a hint that strategy might be something cool. We wanted to end up with something big. What about the history of Civilization? We were inspired by SimCity with god games. The core was a number of simple systems: economic, combat, growth. Everything was understandable on its own. Once it all interacted, the decisions for the player became very interesting.”

When Civilization 2 released, the developer projected 38,000 copies to be sold. However, it did much better, a fact which Meier credits mod support for. “So many [of the player’s] ideas and energy has gone into the game. Brian [Reynolds] introduced the idea of modding into Civ II, and the game took off. “Something about Civ seems to bring out the game designer in people.”

Thus far there have been 66 different versions of Civilization released across all platforms and of the 33 million copies sold in the series’ history, Civilization 5 and its expansions contributed to 8 million. It also seems that players have spent more than 1 billion hours playing the game as per Steam stats and sales.