A Denarius coin is a special resource which allows you to hire a special class of Units — Roman Warriors. When you have enough Denarii, you are able to hire Gladiators, Velites, Triarii and Legionnaires.
To receive Denarii, you must first go to the Argentarium to trade Bronze and Timber.
Go to the Argentarium to begin exchanging Resources for Denarii. The amount of Resources you choose to exchange is completely up to you. Exchange both 500 Bronze and 500 Timber, and in 1 hour you will receive 500 Denarii. The exchange ratio is always the same; however, selecting shorter periods of time will increase the speed at which your trades are returned and you are rewarded with Denarii. Simply choose the desired number of Denarii and click the "Exchange" button.
You may also choose to spend Drachmas to instantly exchange Resources for Denarii by choosing the desired number of Denarii you wish to receive and clicking the "Purchase" button. For instantaneous exchange, you will need Drachmas as well as both Bronze and Timber.
Once you've signed the required Agreements and saved enough Denarii, you will be able to hire Gladiators, Velites, Triarii, and Legionnaires. These Units can be hired via the Units menu.
The number of Denarii you can hold is limited by your Warehouse capacity. Upgrade your Warehouses to store more Denarii.