 While oxen were traditionally used as work animals on farms, horses began to be used in greater numbers after the development of the horse collar.Oxen and horses were sometimes harnessed together.The transition from oxen to horses for farm work was documented in pictorial sources (for example, the 11th-century Bayeux tapestry depicts working horses), and also clear from the change from the Roman two-field crop-rotation system to a new three-field system, which increased the cultivation of fodder crops (predominantly oats, barley and beans).