Call of Duty 4: Arches
By One Richard
This tutorial will show you how to create arches (The easy way).
Step 1
First you do is to determine the place you are going to locate the arch. In this case I will do it between these two columns.
Create a brush that will represent the total size of it.
With the brush selected, go to Patch > Primitive > End Cap, this will convert th brush in to a curved patch.
Usually it needs to be rotated and scaled to fit in its place.
When done, just go to patch > Cap.
In the small options windows that pops up just check Inverted Endcap.
The basic structure of the arch is done.