But, there's an article here on GDNet at http://www.gamedev.net/reference/programming/graphics3d/article678.asp that discusses only one of the many ways of doing terrain. As you get more advanced and consider doing your own 3D terrain stuff, there are a bunch of papers on mesh optimizations, visibility, landscape creation, etc available around the web. I'd actually like to get all the ones I've collected put on GDNet, but I don't know if our server has the space. ;-)
Anyways, check out that article for a little insight into the whole 3D terrain thing. It's definitely not the only way of doing things and most likely not the way a game like Battlezone renders terrain, but it's a start.
Kevin