Neustria and Aquitaine, was for all practical purposes the border-land also of Neustria and of Britanny. Angers, with its Roman citadel and its Roman walls, perched on the crest of its black slate-rock, at once guarding and guarded by the two rivers which flowed round its foot, was a far mightier fortress than Nantes; Angers, rather than Nantes, was the true key of the Loire valley, and the stronghold of the Neustrian border against all attacks from the west, whether by land or by sea. In the first days of Charles the Bald, when the new king was struggling with his brothers, and the pirate ships were beginning again to strike terror into the coasts of Gaul, Lambert, a Breton-born count of the Angevin march, sought from Charles the investiture of the neighbouring and recently-vacated county of Nantes. On the refusal of his demand, he threw off his allegiance, offered his services to the Breton king Nomenoë, and on failing to obtain the coveted prize by his help, called in that of a pirate fleet which was cruising about the shores of Britanny. It was thus at the invitation and under the guidance of a man who had been specially intrusted with its defence that the northmen made their first entrance into the hitherto peaceful estuary of the Loire. Nantes was stormed and sacked;[235] the desolate city was left in the hands of Lambert and the Bretons, and the ravagers sailed away, probably to swell the forces and share the spoil of a fleet which in the following year made its way to the estuary of the Garonne, and pushed inland as far as Toulouse. Nearly ten years passed away before the northmen repeated their dash upon central Gaul. The valley of the Seine and the city of Paris were the victims of their next great expedition, in 845; and a series of plundering raids upon the Aquitanian coast were crowned in 848 by the conquest of Bordeaux. For a moment, in 851, the fury of the pirates’ attack seemed to be turning away from Gaul to spend itself on Britain; but a great victory of the West-Saxons under Æthelwulf at Aclea threw them back upon their old field of operations across the Channel, and in the terror of their threatened onset Charles sought to detach the Bretons from their alliance by a formal cession of the counties of Rennes and Nantes and the district west of the Mayenne, which had passed into Breton hands by the treason of Count Lambert.[236] His precautions failed to avert the blow which he dreaded. Next year the pirates made their way back again round the Armorican coast, up the mouth of the Loire, past Nantes, and through the Angevin march--now shrunk to a little corner of territory wedged in between the Mayenne and the Loire--as far inland as Tours, where they sacked and burned the abbey of S. Martin and drove its canons into exile with the hardly-rescued body of their patron saint.[237]