During the canal days, mules walked the towpath and pulled heavy boats, hauling sixty tons or more of freight. They worked in teams of two or three, and cargo boats had a middle cabin to stable a second team so the teams could switch every six hours. Mules were valued for their endurance, caution, resistance to mouth and harness sores, and lower feed costs, while horses were faster and were used on early passenger boats when speed mattered more than endurance. A mule's intelligence came from its donkey father and its athletic ability from its horse mother.