During the whole of the ensuing winter the war was carried on in England without intermission, whilst, with the singular policy of the age, a truce existed in all other quarters; thus enabling the partizans of Henry, in his own kingdom, to unite their forces for the purpose of crushing the Earl of Leicester.[403] [Sidenote: A. D. 1174.] At the expiration of the truce in January, the payment of 300 marks, offered by the barons of Northumberland through the medium of the bishop of Durham, purchased from William a further cessation of hostilities until Easter; and when the term of this second truce had also expired, the armies of the allies[404] at length appeared in the field. Whilst Louis prosecuted the war in Normandy, and the Count of Flanders, with the younger Henry, meditated a descent upon England, William again crossed the Borders with an army, strengthened by a body of mercenaries from the Low Countries;[405] his brother David proceeding at once to the south, as the earl had been chosen to command the English confederates, now left without a head through the capture of the Earl of Leicester.[406] Leaving a division of his army to blockade Carlisle, William led the main body into Northumberland. Brough and Appleby were captured without resistance, and the castles of Liddel, Warkworth, and Harbottle, fell, in succession, into the hands of the Scots, who then retraced their steps to Carlisle. A close blockade extorted a promise of surrender from the castellan, Robert de Vaux, if no relief arrived before Michaelmas; for his provisions were beginning to fail, and he suspected the townsmen--attached, probably, to the memory of David, who had often made Carlisle his residence--of a favourable inclination towards the Scots. William then marched to invest Prudhoe Castle, upon the southern bank of the Tyne, where he was joined by Robert de Mowbray, the youngest of the victors of Northallerton, who, sorely pressed by the warlike bishop of Lincoln, eagerly advocated the advance of the Scots into Yorkshire, before the fall of his last castle of Thirsk, placing his eldest son in the hands of William as a hostage for the sincerity of his request. William promised to march to his assistance, but, warned of the approach of the Yorkshire barons, he relinquished his intention of relieving Thirsk, and, raising the siege of Prudhoe Castle, commenced his retreat towards the north.[407]