I have an idea for caravans. The idea is that you can use caravans to transport a resource from one city to the other. For example, you could let a caravan transport grain, materials, or essence from a small village to your capital city.

It can have nice effects in strategy. For example, destroying caravans can completely mess up the economy of your opponent. Or maybe caravans are not actually destroyed, but captured instead, giving the resources to one of your own cities for a certain duration.

This idea would work even better if cities have a local stock of grain, materials and essence, because in that case you can really have transport armies that carry expensive cargo worth capturing.