These are Civ1-style quadratic tiles. While most of the flat ground and terrain tiles are taken from the FreeCiv Trident tileset by Tatu Rissanen, the unit and resource tiles are original artwork by Richard Heggland.
Most of these were drawn by the CivQuest team, and a few were taken from FreeCiv.
If you'd like to do some graphics for CivQuest, get in touch!
Here is our screenshots collection.