The third is medicine, or leechcraft, which science consists in the art of preserving health, and bringing back the lost health, or in preventing the disease from spreading. All this depends on history, for the physician must gain his knowledge from the ancients, must know what is the cause of diseases, what medicine and treatment to give, what the property and strength of each medicine is, all of which no man could find out in a hundred years through his own experience and investigation. But to experiment on the sick is a dangerous matter, from which they could easily be ruined, though this is not infrequently the case with certain ignoramuses. I shall not mention many other parts of philosophy, but I may summarise by saying that all philosophy is based on history and supported by it, for all the right and wrong and faulty opinions which we find with the ancients are history as regards our knowledge, and form the basis for our corrections. Statesmanship is composed of three different parts: of the internal government, or economy, external relations, and military affairs. All three demand not less history than the other sciences, and without it cannot be perfect. Thus, in political economy it is necessary to know what has caused ruin in former days: how it has been warded off or minimised; what have been the favourable influences; how obtained and preserved, so that the present and future may be wisely judged in the light of that knowledge. On account of this wisdom, the ancient Romans represented their god Janus with two faces, for he knew perfectly the past, and from its examples wisely judged the future. For the administration of foreign affairs it is necessary to know not only one’s own country, but also other governments: what conditions they have formerly been in; what has brought about changes in them; what states they are in now; with whom they have had disputes and wars, and for what; what treaties have been made and confirmed with them, in order to proceed intelligently in the acts at hand. For military leaders it is very important to know by what device and cunning great forces of the enemy have been vanquished, or kept from victory, and so forth, as we see Alexander the Great having held Homer’s books on the Trojan war in great respect, and having been instructed by them. For this reason many great generals have described their own acts and those of others. Of these the most illustrious example is Julius Cæsar, who has described his wars, that future generals might after him use his acts for their own examples, and many famous generals on land and on the sea have followed in his footsteps by writing of their exploits. Many great rulers have either themselves written of their acts, or have ordered expert people to write of them, not only that their memory should live in glory, but that their descendants should have examples to follow.