Attached Link: Ishtar Gate Archway - How to model?

I am building a model of the Babylonian "Ishtar Gate", and the top portion of the gate has an archway (see picture). I am not sure the best way to build a model of that part that I can then apply this texture map to, and have the cut-out gateway line up just right with the texture map. My initial thought was to make a transparency map based on the texture map, and apply both to a solid rectangular block, using mapping on the face of a surface. This did not seem to work in Carrara (Texture looked okay, but there was no "cutout"). Any ideas?