Carts are the cheapest and most basic type of Transportation Unit / vehicle. Many more buildings can craft and store them than Boats, Ships or Trains. They also require no Research prerequisites to build ranked 1 Carts. These simple wheeled constructions can seriously improve your storage and trading without breaking the bank.
Construction / Recruiting
Carts, even high ranking Carts, are made only of Hemp. This means that building owners with very limited production access can usually put together enough to make some kind of Cart. Small as they can start, Carts still require crew to manage, especially if you plan to send them trading and raiding.
Carts can be sent on predictable journeys to known locations in order to bring back a share of the local goods. It should be noted that Cars cannot be sent to any region outside their own so the trade rewards they bring back are limited to those provided by their home region. Carts auto trading require small crews which never include Peers. They are more likely to bring back Resources than Goods, and even less likely to return full of currency. The consistent banditry along trade routes ensures that your Cart is always in some danger of being attacked and never returning.
In the ancient tradition of land-based banditry, Carts can be sent to auto-raid their neighbors. Remember that you still can't leave your home region so rewards (and victims) will all be in the same area you live. Carts have the shortest of all transport raiding cycles and the lowest chance to intercept.
Construction and Storage Buildings
There are many buildings in the game that can either store or build carts. The Cargo Dock and Lodge can do both at the same time. These are very common forms of transportation and are expected to serve many purposes in a settlement. If allowed to, players will buy lots and build places to construct and store their Carts and rent extra Cart storage to their neighbors.