Du Plessis-Mornay, a young Huguenot gentleman of twenty-three, of marked literary ability and destined to be the intellectual leader of the Protestants in coming years, who had lately traveled through the Netherlands and visited England,[1518] in collaboration with the admiral drew up a remarkable memorial advocating French intervention in the Low Countries,[1519] which Coligny presented to the King. English and French volunteers soon poured into the land.[1520] Louis of Nassau left for Valenciennes, which had successfully revolted, accompanied by La Noue and Genlis.[1521] On May 24, by a stratagem, Genlis secured possession of Mons, one of the most important fortresses to Spain in the Low Countries in the present state of mind that France was in.[1522] From this point of vantage he wrote hopefully to Charles IX for more soldiers, a “good minister,” a surgeon, some cannon founders, and drugs.[1523] While these events were happening on land, on the sea the Zealanders attacked and dispersed the Spanish fleet in the Sluys on June 8, and seized twenty merchantmen under its convoy:[1524] and, to the elation of France,[1525] far down in the Bay of Biscay the fleet of Flushing three days later scattered another of Spain’s armadas.[1526] All Holland, Amsterdam and Rotterdam excepted, was lost to Spain.[1527] Sir Humphrey Gilbert with 1,200 English and some French and Walloons landed in the Low Countries, on July 10, and captured Sluys and Bruges.[1528] Money poured in upon William of Orange, who in June went to Frankfurt to purchase supplies and enlist men.[1529] The duke of Alva was in desperate straits. The Walloons everywhere in the army mutinied and deserted, and he was short of munitions.[1530] But such successes were too great to last. Louis of Nassau found he could not hope to hold Mons for long with the slender forces at his command and sent Genlis back to France for reinforcements. Charles IX, under pressure from Coligny, provided men and money secretly, but Genlis’ relief column was intercepted on July 16 and captured by the duke of Alva.[1531] It was only a question of time before Mons surrendered.[1532] The blow was a heavy one to France. It mattered little to France that French subjects were killed or taken prisoner during the siege. But it was of tremendous consequence to France that Alva found on Genlis’ person a letter written by Charles IX to Louis of Nassau on April 27, 1572, in which the King said that he was resolved as soon as the condition of affairs at home permitted him, to employ the armies of France for the liberation of the Low Countries.[1533] Well might Alva’s secretary write “I have in my possession a letter of the king of France which would strike you with astonishment if you could see it.”[1534] Spain possessed indubitable proof at last of French duplicity.