Notwithstanding the loss of so many fortresses on the endangered frontier of his territory, Louis XIV. was so much encouraged by what he knew of the great change which was going on in the councils of Queen Anne, that, expecting daily an entire revolution in the ministry, and overthrow of the war party in the Cabinet, he resolved on the most vigorous prosecution of the contest. He made clandestine overtures to the secret advisers of the Queen, in the hope of establishing that separate negotiation which at no distant period proved so successful. Torcy, the Duke's enemy, triumphantly declared, "what we lose in Flanders, we shall gain in England."[14] To frustrate these machinations, and if possible rouse the national feeling more strongly in favour of a vigorous prosecution of the war, Marlborough determined to lay siege to Aire and St Venant, which, though off the line of direct attack on France, laid open the way to Calais, which, if supported at home, he hoped to reduce before the conclusion of the campaign.[15] He entertained the most sanguine hopes of success from this design, which was warmly supported by Godolphin; but he obtained at this time such discouraging accounts of the precarious condition of his influence at court, that he justly concluded he would not be adequately supported in them from England, from which the main supplies for the enterprise must be drawn. He wisely, therefore, resolved, in concert with Eugene, to forego this dazzling but perilous project for the present, and to content himself with the solid advantages, unattended with risk, of reducing Aire and St Venant.
Having takes their resolution, the confederate generals began their march in the beginning of September, and on the 6th of that month, both places were invested. Aire, which is comparatively of small extent, was garrisoned by only five thousand seven hundred men; but Venant was a place of great size and strength, and had a garrison of fourteen battalions of foot and three regiments of dragoons, mustering eight thousand combatants. They were under the command of the Count de Guebriant, a brave and skillful commander. Both were protected by inundations, which retarded extremely the operations of the besiegers, the more especially as the autumnal rains had early set in this year with more than usual severity. While anxiously awaiting the cessation of this obstacle, and the arrival of a great convoy of heavy cannon and ammunition which was coming up from Ghent, the Allied generals received the disheartening intelligence of the total defeat of this important convoy, which, though guarded by sixteen hundred men, was attacked and destroyed by a French corps on the 19th September. This loss affected Marlborough the more sensibly, that it was the first disaster of moment which had befallen him during nine years of incessant warfare.[16] But, notwithstanding this disaster, St Venant was so severely pressed by the fire of the besiegers, under the Prince of Anhalt, who conducted the operations with uncommon vigour and ability, that it was compelled to capitulate on the 29th, on condition of its garrison being conducted to St Omer, not to serve again till regularly exchanged.