The masters do not make, however, the mistake of advocating a passive defensive. Suntzu lays down that the division of the forces which this strategy involves, is to be everywhere weak, rendering the army liable to be taken in detail by the concentrated forces of the enemy. It is rather the defence which avoids battle by mobility and manoeuvre, induces the enemy by stratagem to divide his forces, or act in conformity with our wishes, and then falls upon him. With regard to the tactics of the battlefield, the pitched battle, or, in other words, the frontal attack, is considered unworthy of the skilful general. The plan of attack should consist, broadly speaking, in the division of the army into two forces. The enemy is "attracted and engaged by one force, and defeated with the other;" and here we have the containing or secondary attack, and the main or reserve force which decides the battle of to-day--a most striking instance of the continuity of military principles. Considerable space is devoted to the influence of ground on war. The passage of defiles and rivers is still conducted in the same way. The many large rivers of China naturally affected military operations; and, among other axioms, it is laid down that the passage of a river should not be disputed, as the enemy will probably give up the attempt, and make the passage untouched at some other point, but that he should be attacked when half his force is across the stream. Again, an army should not encamp on a river below the enemy, as it is thereby liable to be inundated, or to have its water poisoned; or the enemy may come down stream and make a sudden attack. While both writers were professional soldiers, they show a fine disinterestedness by repeatedly pointing out that even successful war brings evil in its train. Wu remarks that "few are those who have gained power on earth by many victories," and he is insistent that war should not be undertaken until a careful comparison of the two sides shows that victory is certain; and he adds, "The army which conquers makes certain of victory and then attacks, while the army that is defeated fights in the hope of success." Hence the importance they assign to intelligence of the enemy, and to the spy; and as the sages dealt with war between members of the same race, the work of spies was greatly facilitated. The spy was treated with great honour by his countrymen, and the fact that many of the national heroes of China were spies, shows that the part that they played was not forgotten. They frequently toiled for years, and rose to high rank in the enemy's service; and thus, by wrong counsel and by spreading mistrust in his ranks, they became a two-edged sword in the hands of the general. "Wonderful, indeed, is their power," exclaims Sun; but he also reminds us that their management is the most difficult and delicate duty of the general. II