The year 876 marked the end of the truce and the renewal of the Danish attacks on Wessex. Three Danish kings, one of whom was the famous Guthrum, after wintering in Cambridge, stole past the West Saxon _fyrd_, and apparently by a series of night marches succeeded in reaching Wareham. Here, surrounded by the rivers Piddle and Frome, they could feel themselves as secure as in the islands of Thanet or Sheppey. Worsted, however, by blockade rather than by battle, the Danish kings came to terms with Alfred. They gave hostages once more of their most honourable men and swore upon a certain sacred armlet--an oath, says the chronicler, which they had never given to any other people--that they would truly depart out of the kingdom. Not all of “the army,” however, kept this solemn compact. Hostages and oath notwithstanding, the mounted men rode off to Exeter and entrenched themselves there. King Alfred’s pursuit with the infantry of the _fyrd_ was vain. Fortunately, however, the fleet which should have co-operated with the Danes was overtaken by a fierce storm, and 120 ships filled with warriors were dashed to pieces on the rocks of Purbeck. Disheartened by this calamity, the Northmen at Exeter once more swore great oaths, gave hostages and marched forth from Wessex to their own now vassal kingdom of Mercia. This happened in the autumn of 877. Soon after Twelfth night, at the beginning of 878, another gang of plunderers came suddenly to the “royal villa” of Chippenham, probably hoping to capture the king himself. With a small band of followers Alfred escaped to the woods and morasses of Athelney in Somerset; but though they thus missed their chief prize, this invasion of Wessex, for some reason unknown to us, came nearer to success than any which had preceded it. From Chippenham as a centre the Danes harried the country far and wide; they drove many of the inhabitants across the sea; those who remained had to accept them as their lords; it seemed as if Wessex would have to follow the example of Mercia and Northumbria, and bow its neck to the Danish yoke. Meanwhile Alfred, in the little island of Athelney--an island then, because surrounded on all sides by marshes, but an island now no longer--was gathering his faithful followers round him and quietly preparing for the recovery of his throne.[133] The little band of his followers wrought at the construction of a rude fortress, which was finished by Easter, and which proved impregnable by the heathen assailants. Behind this earthwork the West Saxon king “greatly stood at bay,” and from hence he and the men of the Somerset _fyrd_, who gathered round him under their ealdorman Ethelnoth, made several successful sallies against the enemy.