Circus building for romans, so the level before colosseum, gives too little public order increase to be worth it of upgrading. It increases the previous +12 public order to +15 only, little increase in money (from 150, to 270) and a penalty of food of -10 (previous level is -4). Colesseum is instead a big jump in positive aspects (-10 food, +500 wealth, +24 po). I would suggest the following changes to make "circus" more balanced: -8 food, +18 public order, +300 wealth.
It will make circus more convenient to build for sure.