Though from a strategical point of view the plan set forth in Bonaparte's instructions to Masséna possessed many advantages, yet it had one great defect. With the main bulk of Masséna's forces concentrated at Genoa, and with small detachments holding the line of the Apennines and Maritime Alps, it is evident that Melas could force his way across the mountains between Genoa and the Tenda Pass, and thus cut the communications of Masséna and enclose him in Genoa. It is evident, too, that Melas could surround Masséna and eventually force him to capitulate. The French might fight desperately and hold out for months; yet, in time, they would be compelled to yield. The histories of wars and of sieges show that, when a commander allows himself to be enclosed in a fortification, he is doomed to defeat in the end. "_Great armies_," says Von der Goltz, "_which are shut up in a fortress after lost battles, are, as the history of investments from Alesia down to Metz proves, almost always lost_." Again he says: "Among all the relations between fortress and field army, the latter must make it a supreme rule _never to allow itself to be thrown into a fortress_. Even to pass through it is dangerous, because the army may be kept prisoner there against its will. _Fortresses protect the troops they contain, but, at the same time, anchor them to the spot. An army can easily be got behind fortifications, but only with difficulty back again into the open field, unless it be that strong help from without lends it a hand._" When the commander of an army is hard pressed, and there is near at hand a strongly fortified place with outlying works of great strength, and provisions and water within, the temptation is great to seek security there. Second rate generals accept such opportunities, but in doing so they make fatal mistakes. The great masters of the art of war manoeuvre for position, and become themselves the besiegers, or decide upon the open battle-field the fate of their fortresses and their armies.