Once arrived in the provinces committed to his charge, he had no choice but to continue the war. But on January 27, 1574, Orange conquered Middelburg and from that date the Spanish flag ceased to float over any portion of the soil of Holland or Zeeland. In open battle at Mook, however, [Sidenote: April 14, 1574] the Spanish veterans again achieved success, defeating the patriots under Louis of Nassau, who lost his life. The beginning of the year saw the investment of Leyden in great force. The heroism of the defence has become proverbial. When, in September, the dykes were cut to admit the sea, so that the vessels of the Beggars were able to sail to the relief of the city, the siege was raised. It was the first important military victory for the patriots and marks the turning-point of the revolt. Henceforth the Netherlands could not be wholly subdued. Requesens summoned the States General and offered a pardon to all who would submit. But the people saw in this only a sign of weakness. A flood of pamphlets calling to arms replied to the advances of the government. Among the pamphleteers the ablest was Philip van Marnix, [Sidenote: Marnix, 1538-98] a Calvinist who turned his powers of satire against Spain and the Catholic {264} church. William of Orange, now a Protestant, living at Delft, inspired the whole movement. Requesens, believing that if he were out of the way the revolt would collapse, like Alva offered public rewards for his assassination. That there was really no common ground was proved at a conference between the two foes, broken off without result. In the campaign of 1575 the Spanish army again achieved great things, taking Oudewater, Schoonhoven and other places. But the rebels would not give up. [Sidenote: March 5, 1576] The situation was changed by the death of Requesens. Before his successor could be appointed events moved rapidly. After taking Zierikzee on June 29, the Spanish army turned to Aalst, quartered the soldiers on the inhabitants, and forced the loyal city to pay the full costs of their maintenance. If even the Catholics were alienated by this, the Protestants went so far as to preach that any Spaniard might be murdered without sin. In the concerted action against Spain the Estates of Brabant now took the leading part; meeting at Brussels they intimidated the Council of State and raised an army of 3000 men. By this time Holland and Zeeland were to all intents and purposes an independent state. The Calvinists, strong among the native population, were recruited by a vast influx of immigrants from other Provinces until theirs became the dominant religion. Holland and Zeeland pursued a separate military and financial policy. Alone among the provinces they were prosperous, for they had command of the rich sea-borne commerce.