Units

Storage Unit
These are units you can buy to increase your caravan storage size.

Special Unit
Units that have the ability to cary goods, steal, spy etc.

A carrier an carry goods from locations your not present to your caravan. The number of carriers is limited to half the number of villages you have. Tip: if you can buy a new carrier the limmit isn't implemented (only if you open the screen). So if you can buy a carrier you can buy an unlimmited amount (so if you can, don't just buy a few carriers but make sure you buy 40 carriers. Because of the village limit of 40 you can normally have max 20 carriers)

Combat Unit
Combating units