In this, as in so many other Irish insurrections, there was no want of double traitors; of men who had neither the constancy to remain loyal nor the courage to persevere in rebellion. Many of the arrows shot over the walls were headless, and some bore letters which revealed to the garrison every plan of the besiegers. The children of the citizens, whom he had hitherto detained as hostages, could now be of no use to Offaly, and he exchanged them for some of his own men who had been captured. He tried to get money, ammunition, and other help from the citizens in return for raising the siege; but the men of Dublin knew their advantage, and answered that they had no money to spare. They argued that if his intentions were loyal he had no need of warlike stores, and that to supply him might be to make a rod for their own backs. They were, however, willing to supply him with enough parchment to engross his pardon upon, and to join him in begging humbly for it. Having neither powder nor shot, Offaly could not retort to any purpose, and he withdrew to put his ancestral castle of Maynooth in a posture of defence.[135] [Sidenote: Reinforcements arrive from England.] Besides retaining some of the citizens' children, the rebels had captured Chief Justice Luttrell and Lord Howth. A truce was therefore concluded for six weeks, but Offaly broke it within twenty-four hours by burning corn belonging to the Prior of Kilmainham. Meanwhile Skeffington had sailed from North Wales. The bulk of his fleet and army were intended for Waterford, but Sir William Brereton and Captain Salisbury were detached with 400 men for the relief of Dublin. Brereton took command of the city, and saw that proper watch was kept. Shortly afterwards eighty Northern spearmen under Musgrave and Hamerton landed or were driven ashore at Clontarf, where the rebels met them in great force. They were perhaps picked men, for their white coats and red crosses are particularly mentioned: at all events, they made a gallant resistance, and Offaly was wounded. Musgrave and Hamerton were both killed, and the rebel chief is said to have mourned deeply for the former, who was his cousin. The main force of the insurgents hung about the Hill of Howth in hope of preventing other English troops from landing, and Brode, Purcell, and Rookes cruised in the offing with their piratical vessels.[136] [Sidenote: Arrival of Skeffington.]