Matte board city.... Not sure why i started with matte board.. it was probably just cause i had it laying around. I just used an X-acto blade and ruler and started cutting then glued them with school glue.. clear works best now that they have it. For pyramids i'd just measure squares a tiny bit smaller than the next depending on how steep i wanted them. Round buildings same thing but octogons (or more sides). The coliseum was built around a segment of toilet paper tubing. The mountains are papier-mache clumps, shaped and dried then covered with a few layers of strip papier-mache. I put too much paste on the last base and it flaked which is why i'm having to redo it after all this time.