The force employed for containing the citadel and for prosecuting its siege had no necessity to be very large.
It was warfare of a terrible kind. Men met underground in the mines, were burned alive when these were sprung, were exhausted, sometimes to death, in the subterranean and perilous labour. The mass of the army was free to menace Villars and his main body.
But the admirable engineering which had instructed and completed the lines of La Bassée still checked the allies, in spite of superior numbers and provisionment still superior.
The effect of the harvest was indeed just beginning to be felt, and the French general was beginning to have a little more elbow-room, so to speak, for the disposition of his men through the gradual replenishment of his stores. But even so, Marlborough and Eugene had very greatly the advantage of him in this respect.
When the siege of the citadel of Tournai had been proceeding a little more than a week, upon the 8th of August the main body of the allies fell suddenly upon Marchiennes. Here the river Scarpe defended the main French positions. The town itself lay upon the further bank like a bastion. The attack was made under Tilly, and, consonantly to the strength of all Villars' defensive positions, that attack failed. On the night of the 9th Tilly retired from before Marchiennes, after having suffered the loss of but a few of his men.
This action, though but a detail in the campaign, is well worth noting, because it exhibits in a sort of section, as it were, the causes of Malplaquet.
Malplaquet, as we shall see in a moment, was fought simply because it had been impossible to pierce Villars' line, and Malplaquet, though a victory, was a sterile victory, more useful to the defeated than to the victors, because the defence had been kept up for such a length of time and was able to choose its own terrain.
Now all this character in the campaign preceding the battle is exemplified in the attempt upon Marchiennes upon August 8th and 9th and its failure. Had it succeeded, had the line been pierced, there would have been no "block" at Malplaquet but an immediate invasion of France, just as there would have been had the line been pierced in the first attempt of five weeks before.