Roman Legion said:
yes, I own C3C, and what are landmark Terrains?
Land mark terrain are terrain that are different versions of a preexisting terrain.
They can be modified for their looks, movement cost, shield/food/commerce output, but they share the same disease factors, city/colony build option, and impassable to wheeled/impassable to all options.
For example, in the War of the Worlds mod, the regular everyday forest was a Land Mark terrain, while the regular forest was replaced with "red weed", so that you can cut down regular forests, and plant the more productive red weed, available only to the martians.
Another example, is in the Playground Mod. The LM mountain was modified into Walls, changing it's graphic to a wall, and movement cost to 1000, and production to zero. Unfortunatly, it can not be impassable, as normal mountains exist, so it was designated with a 1000% defense bonus, and walls with 1000 defense, and immobile, owned by barbarians were placed upon them.