Here's good news if you're still playing Civilization III: following the closure of GameSpy last year, the game now has Steamworks multiplayer support. Publisher 2K Games promised the transition in April last year, but now it's finally happened.
The update can be downloaded now on Steam, with multiplayer functioning exactly as it used to, except you won't have the option to connect with a 'Direct IP' anymore. Meanwhile, save game data will not be affected, but if you happen to own a disc copy of Civilization III (read: not a Steam version) then you'll need to contact 2K support for info on how to make the jump.
It's good timing: creator Sid Meier was the star of last week's PC Gamer show, where he discussed the history of 'Sid Meier' games, in particular the Civilization series.