Moreover, she possessed a line of posts in Spanish Flanders extending from Dunkirk to the Meuse. On the Lys she had Aire and Menin; on the Scarpe, Douay; on the Upper Scheldt, Cambray, Bouchain, Valenciennes, and Condé; on the Sambre, Maubeuge; between Sambre and Meuse, Philippeville and Marienburg; and on the Meuse, Dînant. Further, in the one space where the frontier was not covered by a friendly river, between the sea and the Scheldt, the French had constructed fortified lines from the sea to Menin and from thence to the Scheldt at Espierre. Thus with their frontier covered, with a place of arms on every river, with secrecy and with unity of purpose, the French enjoyed the approximate certainty of being able to take the field in every campaign before the Allies could be collected to oppose them.
1691. The campaign of 1691 happily typifies the relative positions of the combatants in almost every respect. The French concentrated ten thousand men on the Lys. This was sufficient to paralyse all the garrisons of the Allies on and about the river. They posted another corps on the Moselle, which threatened the territory of Cleves. Now Cleves was the property of the Elector of Brandenburg, and it was not to be expected that he should allow his contingent of troops to join King William at the general rendezvous at Brussels, and suffer the French to play havoc among his possessions. Thus the Prussian contingent likewise was paralysed. So while William was still ordering his troops to concentrate at Brussels, Boufflers, who had been making preparations all the winter, suddenly marched up from Maubeuge and, before William was aware that he was in motion, had besieged Mons. The fortress presently surrendered after a feeble resistance, and the line of the Allies' frontier
