For the angled walls, I built a 'frame' for the bricks to rest in. Really that just means there is a 1-brick wide slot through the surrounding bricks. The wall section is at a 45-degree angle and you just have to build the 'frame' in enough so the jagged edge does not show.
Two problems with building this style of wall, I've learned. First is it takes a lot of bricks. Second is the black stripes are not really (a) the same width and (b) the same length, etc. So, the X's in the wall don't look quite as good as I'd hoped. In the Brickshelf gallery there is a pic of the back of the gateway where I hoped you could see the detail a bit better. Here is the pic and the link: [url]http://www.brickshelf.com/cgi-bin/gallery.cgi?f=65317