The necessary Orders were now despatched for the concentration of the Grand Army; and in order to mask its movements as much as possible, the whole line of the Belgian frontier was studded with numerous Detachments of the National Guards furnished by the garrisons of the fortresses, more especially along that part of the frontier which passes in advance of Valenciennes, Condé, Lille, and even as far as Dunkirk; all the _debouchés_ of which line were strongly occupied, the Outposts tripled, and there was every apparent indication that either the principal attack, or at least a formidable diversion, was in course of preparation in that quarter. These measures had the effect of strengthening the anticipations which WELLINGTON had previously formed of offensive movements from the side of Lille and Valenciennes, and consequently of placing him still more upon his guard against any hasty and incautious junction of his forces with those of BLÜCHER, until fully satisfied as to the true direction and object of NAPOLEON's main operations. * * * * * On the 12th of June, Lieutenant Colonel WISSELL, whose Regiment, the 1st Hussars of the King's German Legion, formed an extensive line of Outposts in front of Tournai, reported to Major General Sir HUSSEY VIVIAN, to whose Brigade the Regiment belonged, that he had ascertained, from information on which he could rely, that the French Army had assembled on the frontier, and was prepared to attack. VIVIAN desired him to report upon the subject to Lord HILL, to whose Corps his Regiment was attached while employed on this particular service. The next morning, VIVIAN repaired in person to the Outposts, and found that a French Cavalry Picquet which had previously been posted opposite to Tournai, had a short time before marched to join the main Army, and had been relieved by _Douaniers_. These, upon being spoken to by VIVIAN, did not hesitate to say that their Army was concentrating, and that if the Allies did not advance, their troops would attack. On returning to his Quarters, VIVIAN communicated what he had seen and heard both to Lord HILL and the Earl of UXBRIDGE, by whom the circumstances were made known to the Duke of WELLINGTON. His Grace, however, for reasons before stated, did not think the proper moment had arrived for making any alteration in the disposition of his forces. * * * * * GÉRARD's Corps quitted Metz on the 6th of June, with Orders to reach Philippeville by the 14th. The Imperial Guard began its march from Paris on the 8th, and reached Avesnes on the 13th, as did also LOBAU's Corps from Laon. D'ERLON's Corps from Lille, REILLE's Corps from Valenciennes, and VANDAMME's Corps from Mézières, likewise arrived at Maubeuge and Avesnes on the 13th. The four Corps of Reserve Cavalry concentrated upon the Upper Sambre.