Lack of draft animals is often considered to have been an impediment to urban growth in Mesoamerica. Transport, however, was only one of several factors that influenced the growth of cities. This paper contrasts the effects of energetic efficiency differences between horses and human porters with productivity differences between European and Mesoamerican agricultural systems. Depending on strength and nutritional requirements, horses may be from one to five times as efficient as human porters. Furthermore, horses compete with humans for food. Where the horse played a major transport role, one-third of available, arable land was devoted to oat production. With this in mind, I compare maize versus wheat productivity to show that a unit of land in Mesoamerica could support up to twice as many people as the same unit of land in Europe. Thus, the transport advantage enjoyed by European cities is essentially offset by a more intensive agricultural system in Mesoamerica.