In a multiplayer game, we've tried setting up trading, but could not figure out how it worked.

We had a market place, a target market place set, and some resources set in the Trading options, and donkeys and carts available, but this didn't work. The market places are loaded by Settlers, but the donkeys don't start moving.

Does someone have a step-by-step guide how to set up over-land trading with allies using market places? The manual didn't contain any hints on the topic (only contained obvious stuff mentioned above).

thanks!