It consisted of battering-rams and stone-throwing machines, and in this way it was sought to breach the walls. A wooden shelter for the attacking force was constructed and built up to the outer walls of the inland face of the Castle, and under cover of this device the soldiers worked the battering-rams until the defences shook again. The garrison retorted by flinging heavy stones and fire-balls on the shelter, and would either have demolished or burnt it had it not been for an ingenious invention which the French had imported. This consisted of a series of tall wooden towers called _malvoisins_, and ill-neighbours, indeed, they were, for they were established on the edge of the Castle ditch, where, overlooking the outer ward, and being filled with archers whose practice soon slackened the defenders' fire, they would soon have brought the siege to a close, had not the death of the English King removed internal quarrels and aroused a united spirit of patriotism throughout England which boded ill for the prospects of the French prince. The invaders retired from London and the southern counties which they had held, not so much by force of arms as by favour of disaffected Englishmen; they gave up the siege of Dover Castle, and presently re-embarked for France. The struggles between a despotic King and a rapacious nobility which had caused these troubles in the reign of John were soon resumed, and Dover Castle became alternately the hold of one party or the other. The most notable incident in these events was that of 1265, when the Barons held the Castle and had fourteen knights of the King's party imprisoned in the Keep. Prince Edward attacked the Castle from without, and the prisoners, bursting out from their cells and rushing upon their gaolers from within, forced the garrison to surrender. It was in the time of Edward the First that Dover Castle reached its full development. That was the grand era of castle-building in England, when military engineering was practised without reference to ordnance, and had attained to a remarkable ingenuity. Like all Edwardian Castles, that of Dover is concentric and has three wards, enclosed within high curtain walls strengthened with a great number of defensible towers. The outer ward had no less than twenty-seven of these towers, among which the Constable's Tower and gateway is first for size and beauty.