While optional, you can use the GOG GALAXY client for easy installation and library management. Technical Considerations
This was the first entry where your civilization's cultural influence physically pushed back enemy borders. sid-meier-s-civilization-iii-complete-gog
You own the game entirely, with no need for an online connection or client to play. While optional, you can use the GOG GALAXY
For those who prefer a single launcher, you can manually add non-Steam games like this one to your Steam library once installed. Sid Meier's Civilization® III Complete - Error on launch sid-meier-s-civilization-iii-complete-gog