By thus deserting the king at a moment when Henry had every reason to count upon his support, Geoffrey escaped all part in the rout of Mortemer; but the consequence was that when peace was made next year between the king and the duke, one of its clauses authorized William to make any conquests he could at the expense of the count of Anjou.[479] William at once sent warning to Geoffrey to expect him and all his forces at Ambrières within forty days. South of Ambrières, lower down in the valley of the Mayenne, stands the town which bears the same name as the river; its lord, Geoffrey, was the chief man of the district. He went in haste to his namesake and overlord and bitterly complained to him that if these Normans were left unhindered to work their will at Ambrières, the whole land would be at their mercy. “Cast me off as a vile and unworthy lord,” was Martel’s reply, “if thou seest me tamely suffer that which thou fearest!” But the boast was as vain as the challenge before Domfront. William completed without hindrance his fortifications at Ambrières; as soon as his back was turned Geoffrey laid siege to the place, in company with the duke of Aquitaine and Odo, uncle and guardian of the young duke of Britanny; but the mere rumour of William’s approach sufficed to make all three withdraw their troops “with wonderful speed, not to say in trembling flight.” Geoffrey of Mayenne, made prisoner and left to bear alone the whole weight of William’s wrath, took the count of Anjou at his word, and casting off the “vile and unworthy lord” whose desertion had brought him to this strait, owned himself the “man” of the Norman duke.[480] [479] Will. Poitiers (Duchesne, _Hist. Norm. Scriptt._), p. 187. Will. Malm. _Gesta Reg._, l. iii. c. 233 (Hardy, p. 399). [480] Will. Poitiers (Duchesne, _Hist. Norm. Scriptt._), pp. 187, 188.