The Gueux de Mer were at this time most troublesome to the Spaniards, as their small vessels enabled them to penetrate up the rivers and canals. A naval action had been fought (October 11, 1573) on the Zuyder Zee between Count Bossu, who had collected a considerable fleet at Amsterdam, and the patriot admiral Dirkzoon, in which Bossu was completely defeated and taken prisoner. One of the first acts of Requesens was to send a fleet under Sancho Davila, Julian Romero, and Admiral Glimes to the relief of Middelburg, which had been besieged by the patriots upward of eighteen months and was now reduced to the last extremity. Orange visited the Zealand fleet under the command of Louis Boissot (January 20, 1574), and an action ensued a few days later, in which the Spaniards were completely beaten. Requesens himself beheld the action from the lofty dike of Schakerloo, where he stood all day in a drenching rain; and Romero, who had escaped by jumping out of a porthole, swam ashore and landed at the very feet of the Grand Commander. The Hollanders and Zealanders were now masters of the coast, but the Spaniards still held their ground in the interior of Holland. After raising the siege of Alkmaar, they had invested Leyden and cut off all communication between the Dutch cities. The efforts of the patriots were less fortunate on land, where they were no match for the Spanish generals and their veteran troops. It had been arranged that Louis of Nassau should march out of Germany with an army of newly levied recruits and form a junction with his brother William, who was at Bommel on the Waal. Toward the end of February, 1574, Louis encamped within four miles of Maestricht, with the design of taking that town; but finding that he could not accomplish this object, and having suffered some losses, he marched down the right bank of the Meuse to join his brother. When, however, he arrived at Mook, a village on the Meuse a few miles south of Nimwegen, he found himself intercepted by the Spaniards under Davila, who, having outmarched him on the opposite bank, had crossed the river at a lower point on a bridge of boats, and placed himself directly in his path. There was now no alternative but to fight, and battle was delivered on the following day on the heath of Mook, when fortune declared against the patriots. The gallant Louis, seeing that the day was lost, put himself at the head of a little band of troopers, and, accompanied by his brother Henry, and Duke Christopher, son of the Elector Palatine Frederick III, made a desperate charge in which they all perished, and were never heard of more. The only effect of Louis' invasion was to cause the Spaniards to raise the siege of Leyden; before which place, however, they afterward again sat down (May 26th).