Under the new system, which came in by reason of the scarcity of labourers after the two years or so of the Black Death had passed over the land, the lords of the manors found it more to their advantage to let out part of their land--to "farm" it out--to tenant farmers, who paid partly in money and partly in produce, instead of by so many days and pieces of work. The farmers engaged labourers to whom they paid a wage, again part in money and part in kind, of which the amount was settled by Act of Parliament. The modern system, in fact, was established. But another result of this terrible Black Death, which lasted till just after the middle of the fourteenth century, was that the truce between France and England was formally renewed. Troubles on the boundaries of France, however, both in the south and in the west, were constant. Edward, claiming to have a right through his mother to the throne of France, gave the French lords a ready pretext for declining feudal services which they did not wish to render to the king who occupied that throne. Open war was renewed, and both in Normandy and in the south Edward triumphed. The Black Prince, as he was called, King Edward's eldest son, the Prince of Wales, conquered more than all that England claimed in and around the troubadours' Langue d'oc {187} and won the wonderful victory of Poitiers in which he took captive the French king. Again a truce, all in England's favour, was made. Once more war broke out, aroused as usual by the discontent of the French nobles; but this time it was discontent, on the part of those nobles of the south who had long been under the suzerainty of the French king, with the foreign rule of England. We have mentioned two great battles won by the English, Crécy and Poitiers. They deserve a few words more, for they marked a big change in the military story. [Sidenote: Mediæval armour] The ideal of the formidable fighting engine during all the earlier years of those Middle Ages of which we are speaking now, was the knight, in armour clad. Up to the fourteenth century it was armour of mail, that is to say of rings of steel connected with each other and so forming a flexible covering, and yet able to keep out a moderate sword thrust or arrow shot. During the course of the fourteenth century the armour became more solid and weighty, with plates of metal instead of the mail. The horse, as well as the knight, was thus plated, and, so defended, neither could easily be hurt by the weapons then in use. Horse and man together were so heavy that they could bear down, in their charge, a great force of men on foot. Therefore they were so feared that a very small number of the heavy cavalry could put to flight, and to death, a very much larger number of infantry.