Meantime, he received intercepted letters from Verdugo to the Duke of Parma, dated 19th June from Groningen. In these, the Spanish stadholder informed Farnese that the enemy was hovering about his neighbourhood, and that it would be necessary for the duke to take the field in person in considerable force, or that Groningen would be lost, and with it the Spanish forces in the province. He enclosed a memorial of the course proper to be adopted by the duke for his relief. Notwithstanding the strictness by which Philip had tied his great general's hands, Farnese felt the urgency of the situation. By the end of June, accordingly, although full of his measures for marching to the relief of the Leaguers in Normandy, he moved into Gelderland, coming by way of Xanten, Rees, and neighbouring places. Here he paused for a moment perplexed, doubting whether to take the aggressive in Gelderland or to march straight to the relief of Groningen. He decided that it was better for the moment to protect the line of the Waal. Shipping his army accordingly into the Batavian Island or Good-meadow (Bet-uwe), which lies between the two great horns of the Rhine, he laid siege to Fort Knodsenburg, which Maurice had built the year before, on the right bank of the Waal for the purpose of attacking Nymegen. Farnese, knowing that the general of the States was occupied with his whole army far away to the north, and separated from him by two great rivers, wide and deep, and by the whole breadth of that dangerous district called the Foul-meadow (Vel-uwe), and by the vast quagmire known as the Rouvenian morass, which no artillery nor even any organised forces had ever traversed since the beginning of the world, had felt no hesitation in throwing his army in boats across the Waal. He had no doubt of reducing a not very powerful fortress long before relief could be brought to it, and at the same time of disturbing by his presence in Batavia the combinations of his young antagonist in Friesland and Groningen.