A comprehension of this siege of Tournai, which so largely determined the fortunes of the campaign of Malplaquet, will be aided by the accompanying sketch map. Here it is apparent that Marlborough with his headquarters at Willemeau, Eugene with his at Froyennes, the Dutch under Tilly in a semicircle from Antoing to Constantin, completed the investment of the fortress, and that the existing bridge at Antoing which the Dutch commanded, the bridge at Constantin which they had constructed, giving access over the river to the north and to the south, made the circle complete. [Illustration: Sketch Map showing complete investment of Tournai.] The fortifications of Tournai were excellent. Vauban had superintended that piece of engineering in person, and the scheme of the fortifications was remarkable from the strength of the citadel which lay apart from the town (though within its ring of earthworks) to the south. The traveller can still recognise in its abandonment this enormous achievement of Louis XIV.'s sappers, and the opposition it was about to offer to the great hosts of Marlborough and Eugene does almost as much honour to the genius of the French engineer as to the tenacity of the little garrison then defending it. Two factors in the situation must first be appreciated by the reader. The first is that the inferiority of Villars' force made it impossible for him to do more than demonstrate against the army of observation. He was compelled to leave Tournai to its fate, and, indeed, the king in his first instructions, Villars in his reply, had taken it for granted that either that town or Ypres would be besieged and must fall. But the value of a fortress depends not upon its inviolability (for that can never be reckoned with), but upon the length of time during which it can hold out, and in this respect Tournai was to give full measure. Secondly, it must be set down for the allies that their unexpectedly long task was hampered by exceptional weather. Rain fell continually, and though their command of the Scheldt lessened in some degree the problem of transport, rain in those days upon such roads as the allies drew their supplies by was a heavy handicap. The garrison of Tournai numbered thirteen and a half battalions, five detached companies, the complement of gunners necessary for the artillery, and a couple of Irish brigades--in all, counting the depleted condition of the French units at the moment, some six to seven thousand men. Perhaps, counting every combatant and non-combatant attached to the garrison, a full seven thousand men.