The military strength of the castle of the D'Oillys was tested in the struggle between Stephen and the Empress. Driven from London by a rising of its burghers at the very moment when the crown seemed within her grasp, Maud took refuge at Oxford. In the succeeding year Stephen found himself strong enough to attack his rival in her stronghold; his knights swam the river, fell hotly on the garrison which had sallied without the walls to meet them, chased them through the gates, and rushed pell-mell with the fugitives into the city. Houses were burnt and the Jewry sacked; the Jews, if tradition is to be trusted, were forced to raise against the castle the work that still bears the name of "Jews' Mount"; but the strength of its walls foiled the efforts of the besiegers, and the attack died into a close blockade. Maud was however in Stephen's grasp, and neither the loss of other fortresses nor the rigour of the winter could tear the king from his prey. Despairing of relief the Empress at last resolved to break through the enemy's lines. Every stream was frozen and the earth covered with snow, when clad in white and with three knights in white garments as her attendants Maud passed unobserved through the outposts, crossed the Thames upon the ice, and made her way to Abingdon and the fortress of Wallingford. With the surrender which followed the military history of Oxford ceases till the Great Rebellion. Its political history had still to attain its highest reach in the Parliament of De Montfort. The great assemblies held at Oxford under Cnut, Stephen, and Henry III., are each memorable in their way. With the first closed the struggle between Englishman and Dane, with the second closed the conquest of the Norman, with the third began the regular progress of constitutional liberty. The position of the town, on the border between the England that remained to the West-Saxon kings and the England that had become the "Danelagh" of their northern assailants, had from the first pointed it out as the place where a union between Dane and Englishman could best be brought about. The first attempt was foiled by the savage treachery of Æthelred the Unready. The death of Swegen and the return of Cnut to Denmark left an opening for a reconciliation, and Englishmen and Danes gathered at Oxford round the king. But all hope was foiled by the assassination of the Lawmen of the Seven Danish Boroughs, Sigeferth and Morcar, who fell at a banquet by the hand of the minister Eadric, while their followers threw themselves into the tower of St. Frideswide and perished in the flames that consumed it. The overthrow of the English monarchy avenged the treason. But Cnut was of nobler stuff than Æthelred, and his conquest of the realm was followed by the gathering of a new gemote at Oxford to resume the work of reconciliation which Eadric had interrupted. Englishman and Dane agreed to live together as one people