carried equipment and belongings. Common riding horses, often called "hackneys", could be used as pack horses. Cart horses pulled wagons for trading and freight haulage, on farms, or as part of a military campaign. These draught horses were smaller than their modern counterparts; pictorial and archaeological evidence suggests that they were stout but short, approximately , and capable of drawing a load of per horse. Four-wheeled wagons and two-wheeled carts were more common in towns, such as London and, depending on type of vehicle and weight of the load, were usually pulled by teams of two, three, or four horses harnessed in tandem. Starting in the 12th century, in England the use of oxen to pull carts was gradually superseded by the use of horses, a process that extended through the 13th century. This change came because horse-drawn transport moved goods quicker and over greater distances than ox-drawn methods of transport. Agriculture The Romans had used a two-field crop rotation agricultural system, but from the 8th century on, a three-field system became more common. One field would be sown with a winter crop, the second with a spring crop, and the third left fallow. This allowed a greater amount of spring crop of oats to be grown, which provided fodder for horses. Another advance during the Middle Ages was the development of the heavy mouldboard plough, which allowed dense and heavy soils to be tilled easily; this technology required the use of larger teams of draught animals including oxen and horses, as well as the adoption of larger fields. Particularly after the 12th century, the increased use of both the horse collar and use of iron horse shoes allowed horsepower to be directed more efficiently. Horse teams usually were four horses, or perhaps six, as compared to eight oxen, and the lesser numbers compensated for the fact that the horses needed to be fed grain on top of pasture, unlike oxen. The increased speed of horses also allowed more land to be ploughed in a day, with an eight ox plough team averaging half of an acre per day, but a horse team averaged a full acre per day. For farm work, such as ploughing and harrowing, the draught horses utilized for these purposes were, in England, called 'affers' and 'stotts' ( and in medieval Latin). These horses were usually smaller and cheaper than the cart horse. The difference between