So the prince, instead of risking another Nieuport campaign, took the field with a small but well-appointed force, about ten thousand men in all, marched to the Rhine, and early in June, laid siege to Rheinberg. It was his purpose to leave the archduke for the time to break his teeth against the walls of Ostend, while he would himself protect the eastern frontier, over which came regular reinforcements and supplies for the Catholic armies. His works were laid out with his customary precision and neatness. But, standing as usual, like a professor at his blackboard, demonstrating his proposition to the town, he was disturbed in his calculations by the abstraction from his little army of two thousand English troops ordered by the States-General to march to the defence of Ostend. The most mathematical but most obedient of princes, annoyed but not disconcerted, sent off the troops but continued his demonstration. "By this specimen," cried the French envoy, with enthusiasm, "judge of the energy of this little commonwealth. They are besieging Berg with an army of twelve thousand men, a place beyond the frontier, and five days' march from the Hague. They are defending another important place, besieged by the principal forces of the archdukes, and there is good chance of success at both points. They are doing all this too with such a train of equipages of artillery, of munitions, of barks, of ships of war, that I hardly know of a monarch in the world who would not be troubled to furnish such a force of warlike machinery." By the middle of July he sprang a mine under the fortifications, doing much damage and sending into the air a considerable portion of the garrison. Two of the soldiers were blown into his own camp, and one of them, strangely enough, was but slightly injured. Coming as he did through the air at cannon-ball speed, he was of course able to bring the freshest intelligence from the interior of the town. His news as to the condition of the siege confirmed the theory of the stadholder. He persisted in his operations for three weeks longer, and the place was then surrendered. The same terms--moderate and honourable were given to the garrison and the burghers as in all Maurice's victories. Those who liked to stay were at liberty to do so, accepting the prohibition of public worship according to the Roman ritual, but guaranteed against inquisition into household or conscience. The garrison went out with the honours of war, and thus the place, whose military value caused it to change hands almost as frequently as a counter in a game, was once more in possession of the republic. In the course of the following week Maurice laid siege to the city of Meurs, a little farther up the Rhine, which immediately capitulated. Thus the keys to the debatable land of Cleves and Juliers, the scene of the Admiral of Arragon's recent barbarities, were now held by the stadholder.