Robert fulfilled his trust gallantly and successfully till he fell in a Scandinavian ambush at Brissarthe in 866.[240] His territories were given to a cousin of the king, Hugh of Burgundy, who was either so incapable or so careless of their defence that before six years had passed he suffered the very corner-stone of his duchy, the most important point in the whole scheme of operations against the northmen in central Gaul, to fall into the enemies’ hands. A band of pirates, sailing unopposed up the Loire and the Mayenne after Robert’s death, found Angers deserted and defenceless, and settling there with their families, used it as a centre from which they could securely harry all the country round. The bulk of the pirate forces, however, was now concentrated upon a great effort for the conquest of Britain, and while the invaders of Angers lay thus isolated from their brethren across the Channel, Charles the Bald seized his opportunity to attempt the recovery of the city. In concert with the Breton king, Solomon, he gathered his forces for a siege; the Franks encamped on the eastern side of the Mayenne, the Bretons on the opposite shore. Their joint blockade proved unavailing, till one of the Bretons conceived the bold idea of turning the course of the Mayenne, so as to leave the pirate ships stranded and useless. The whole Breton army at once set to work and dug such an enormous trench that the northmen saw their retreat would be hopelessly cut off. In dismay they offered to purchase, at a heavy price, a free withdrawal from Angers and its district; their offer was accepted, and Angers was evacuated accordingly.[241] [240] Ann. Bertin. a. 866 (_Rer. Gall. Scriptt._, vol. vii. p. 94). [241] Regino, a. 873 (Pertz, _Mon. Germ. Hist._, vol. i. pp. 585, 586). Ann. Bertin. and Mettens. and Chron. Namnet. a. 873 (_Rer. Gall. Scriptt._, vol. vii. pp. 117, 200, 220, 221). Chron. Sigebert. a. 875 (_ib._ p. 252). Chron. S. Serg., a. 873. (Marchegay, _Eglises_, pp. 132, 133).