affers and stotts was largely nominal. Medieval English records from south-east England and East Anglia typically use the term 'stott', while 'affer' is used in documents from across the rest of the country. 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). Horses were also used to process crops; they were used to turn the wheels in mills (such as corn mills), and transport crops to market. The change to horse-drawn teams also meant a change in ploughs, as horses were more suited to a wheeled plough, unlike oxen. Equestrian equipment and technological innovations The development of equestrian technology proceeded at a similar pace as the development of horse breeding and utilisation. The changes in warfare during the Early Middle Ages to heavy cavalry both precipitated and relied on the arrival of the stirrup, solid-treed saddle, and horseshoe from other cultures. The development of the nailed horseshoe enabled longer, faster journeys on horseback, particularly in the wetter lands in northern Europe, and were useful for campaigns on varied terrains. By providing protection and support, nailed horse shoes also improved the efficiency of draught horse teams. Though the Romans had developed an iron "hipposandal" that resembled a hoof boot, there is much debate over the actual origins of the nailed horseshoe, though it does appear to be of European origin. There is little evidence of nailed-on shoes prior to AD 500 or 600, though there is speculation that the Celtic Gauls were the first to nail on metal horseshoes. The earliest clear written record of iron horseshoes is a reference to "crescent figured irons and their nails" in a list of cavalry equipment from AD 910. Additional archaeological evidence suggests they were used in Siberia during the 9th and 10th centuries, and had spread to Byzantium soon afterward; by the 11th century, horseshoes were commonly used in Europe. By the time the Crusades began in 1096, horseshoes were widespread and frequently mentioned in various written sources.