When you proceed towards the enemy or he proceeds towards you, the position of your force should be on the approaches high ground or on the edges of mountains or the bends of rivers, so that it may serve you as a help and a place to return to. Your encounter should be from one side or two sides. Place watchers on the peaks of mountains and the raised sides of the high ground so that the enemy may not approach you from any place, whether of danger or safety.
And know that the vanguard of an army serves as their eyes, and the eyes of the vanguard are their informers. Beware of dispersal. When you halt do so together and when you move you should move together. When night comes fix your spears in a circle and do not sleep except for dozing or napping.
 When Amīr al-mu’minīn put Ziyād ibn an-Naḍr al-Ḥārithī and Shurayḥ ibn Hānī al-Ḥārithī in command of contingents of eight thousand and four thousand strong at the camp of an-Nukhaylah and ordered them to advance towards Syria (ash-Shām), some dispute arose between them about their ranks, of which they apprised Amīr al-mu’minīn and wrote letters of complaints about each other. In reply, Amīr al-mu’minīn wrote to them that when they marched jointly the command of the whole force would be with Ziyād ibn an-Naḍr al-Ḥārithī and when they marched separately each would be in command of the force over which he had been placed.
In this letter Amīr al-mu’minīn also wrote for them certain instructions. Here as-Sayyid ar-Raḍī has taken down only the portion containing the instructions. These instructions are not only useful as concerns the strategies of fighting of those days, but their utility and importance in bringing out the principles of fighting in these days also is undeniable. These instructions are that at the time of encounter with the enemy the forces should be encamped on the tops of mountains and turns of rivers, because in this way the low areas of the rivers would serve as trenches and the peaks of mountains as the walls of the fortress and thus it would be possible to feel secure and face the enemy from the other side. Secondly, that the attack should be from one side or at the most from two sides, because by distribution of the entire force on several fronts weakness would inevitably arise. Thirdly, that the watchers should be put in position on the tops of high ground and the peaks of mountains so that they may give warning before the attack. Sometimes it happens that instead of attacking from the expected side the enemy attacks from a different side. Therefore, if watchers are in position in high places they will detect the enemy from the cloud of dust seen from a distance.
To clarify the useful aspect of these instructions Ibn Abi’l-Ḥadīd has recorded (in vol. 15, p. 91) a historical incident that when Qaḥṭabah (ibn Shabīb aṭ-Ṭā’ī) encamped in a village after leaving Khurāsān, he and Khālid ibn Barmak went and sat on the top of a nearby hill. No sooner had they sat down than Khālid noticed flocks of deer coming running from the forest. On seeing this he said to Qaḥṭabah, “O’ commander, get up and announce to the army that they should at once fall in line and take up arms.” Hearing this, Qaḥṭabah was startled and stood up but looking hither and thither said, “I do not see the enemy’s men anywhere.” He replied, “O’ Amīr, this is not the time that should be lost in conversation. You see these deer which are proceeding towards the people, leaving their abodes. This means that the army of the enemy is marching from their rear.” Consequently, he ordered his army to get ready. As soon as the army got ready the noise of horses’ hoofs was heard and within moments the enemy was on them. Since they had prepared themselves for defence in time, they defended themselves against the enemy thoroughly. Now, if Khālid had not been at such a height and had not acted with such sagacity, the enemy would have attacked them unawares and annihilated them. Fourthly, that the reconnaissance should be spread here and there, so that they can be aware of the movements and intentions of the enemy, and thereby foil his plans. Fifthly, that when the army camps it should camp together and when it moves it should move together so that the enemy does not attack you in a state of dispersal and overpower you easily. Sixthly, that at night the guard should be formed by fixing spears in a circle in the ground so that if the enemy attacks in the night, it is possible to prepare for defence by taking up arms at once and if the enemy showers arrows that too can be defied. Seventhly, that deep sleep should be avoided lest you remain unaware of the enemy’s approach and he succeed in attacking you before you get ready.