Caesar III is an absolute classic and you can play it on modern systems, like Linux, with the free and open source game engine Julius which recently had a big new release.
Originally released in 1999, like a lot of classics it is showing some age but a plenty of the gameplay ideas still hold up quite well. The Julius game engine comes with plenty of enhancements like support for high resolution displays and widescreens, support for higher quality audio, plus lots of smaller in-game quality of life fixes you would expect from a modern open source release. Saved games should even be compatible too with the original!
A few days ago Julius 1.2.0 was released upgrading the SDL version used, has an AppImage for Linux gamers giving you an easy way to run it, diagonal scrolling with the keyboard when holding down two arrow keys was added, Aqueduct images are updated when sections are deleted plus a bunch of gameplay and other technical fixes. Support for the game Editor was also improved in this release.