The second point, the so-called “delay” involved in the sieges undertaken by the Allies, proves, when it is put forward, an insufficient acquaintance with contemporary conditions. Any fortress with a considerable garrison left behind untaken would have meant the destruction of the Austrian or Prussian communications, and their destruction at a moment when the Austrian and Prussian forces were actually advancing over a desperately hostile country. Moreover, when acting against forces wholly inferior in discipline and organisation, an untaken fortress is a refuge which one must take peculiar pains to destroy. To throw himself into such a refuge will always stand before the commander of those inferior forces as a last resource. It is a refuge which he will certainly avail himself of ultimately, if it is permitted to him. And when he has so availed himself of it, it means the indefinite survival of an armed organisation in the rear of the advancing invaders. We must conclude, if we are to understand this critical campaign which changed the history of the world, that Coburg did perfectly right in laying siege to one fortress after another before he began what every one expected to be the necessarily successful advance on Paris. The French despair, as one town after another surrendered, is an amply sufficient proof of the excellence of his judgment. We approach the military problem of 1793, therefore, with the following two fields clear before us:-- 1. In the north-east an advance on Paris, the way to which is blocked by a quadrilateral of fortresses: Mons, Maubeuge, Condé, and Valenciennes, with the subsidiary stronghold of Lequesnoy in the neighbourhood of the last. Mons has been in Austrian hands since Dumouriez’ retreat; Condé is just cut off from Valenciennes by Coburg’s advance, but has not fallen; Valenciennes and the neighbouring Lequesnoy are still intact, and so is Maubeuge. All must be reduced before the advance on Paris can begin. Behind these fortresses is a French army incapable as yet of attacking Coburg’s command with any hope of success. Such is the position in the last fortnight of April. 2. Meanwhile, on the Rhine the French garrison in Mayence is besieged; Custine, the French commander in that quarter, has fallen back on the French town of Landau, and is drawing up what are known in history as the Lines of Weissembourg. The accompanying sketch map explains their importance. Reposing upon the two obstacles of the river on the right and the mountains on the left, they fulfilled precisely the same functions as a fortress; and those functions we have just described. Until these lines were carried, the whole of Alsace may be regarded as a fortress defended by the mountains and the river on two sides, and by the Lines of Weissembourg on the third.