(click image to see both frames of the animation)

In max you can create a spline, make it renderable and have it generate a uv. You can then add symetry via a modifier, adjust the mirror's location and you have a 'perfect' arch.

I have been messing around with Geocontrol (http://www.geocontrol2.com/e_index.htm) and pulling the heighmaps into Vue for rendering/texturing.

Pretty simple workflow. I create my terrain in geocontrol and export a bmp heighmap. In Vue I create a terrain and reset it, then load the bmp heighmap. This example is a 4096x map