Denarii are the main currency in Romans: Age of Caesar. They are generated by your houses. The amount that can be accumulated at the Forum and collected is determined by the Forum level and your Denarii Cap which can be increased by Research.
Other ways to acquire Denarii:
You will need Denarii for several actions:
- Recruiting Troops from the Barracks
- Upgrade Buildings (e.g. Forum)
- Buy goods from the Wharves
- Donating to City buildings
TIP: Ranking up and killing barbarian huts will also give you Denarii. Denarii generated from these will let you exceed your Denarii cap.