On the death of Aethelred, Edward took London and Oxford and the parts of Mercia adhering to them into his own hands. Two forts were built on the north and south sides of the Lea at Hertford in 911-12, and another at Witham on the Blackwater in Essex. Edward's work soon bore fruit, for we read that in the same year a large number of those who had been under Danish rule now made submission to the king. The Danes in the Five Boroughs became restless under the continued advance of the English, and twice in the year 913 they made raids from Leicester and Northampton as far as Hook Norton in Oxfordshire and Leighton Buzzard, while in the next year Edward, for the first time in his reign, was troubled by raiders from abroad. Coming from Brittany they sailed up the Severn, ravaged South Wales and the Archenfield district of Herefordshire, but could do nothing against the garrison of Gloucester, Hereford and other neighbouring towns, which seem already to have been fortified. They were forced to leave the district and so careful a watch did Edward keep over the coast of Somerset, Devon and Cornwall that they could make no effective landing, though they tried twice, at Porlock and at Watchet. Ultimately they took up their quarters in the islands of Flatholme and Steepholme in the Bristol Channel, but lack of food soon drove them away to Ireland in a starving condition. In the same year Edward built two forts at Buckingham, one on each side of the Ouse, and his policy again found speedy justification when Earl Thurcytel (O.N. Ðorkell) and all the chief men who 'obeyed[5]' Bedford, together with many of those who 'obeyed' Northampton submitted to him.