And yet the Romans, admitting that they never encountered a tropical climate, seem to have colonized and thriven in countries in which the natives of Western Europe cannot now maintain their ground, cannot keep an army effective in the field for any length of time. The Roman legions and citizens occupied the country of Numidia without an effort; modern France, with an army larger than Rome ever had, can scarcely maintain its position in Algeria. The young population are cut off in their infancy, and it would seem that to maintain a Celtic race in Algeria will test the energies of an empire which it is true formed but a small province of imperial Rome. When we contrast late history with the diffusion of Rome’s armies and citizens over the then known world, we are forced to the conclusion, either that the Italian constitutions of those days were stronger than those of the present inhabitants of Europe, or that the form of civilization presented more safeguards for the protection of health and life. Nothing like the disasters of Varna and the Crimea seems ever to have overtaken the Roman legions who guarded in the time of Trajan the mouths of the Danube and the coasts of the Euxine, or restrained and kept in check the barbarous Moors. Amongst the arts practised by the ancients, but now lost, we must include, I think, the knowledge of that discipline and practical skill by which the Roman, Greek, and even Tartar generals, contrived to keep their armies in the field in health and efficiency, whether storming the castles of Jugurtha, or building walls of defence in that land where English and French troops can neither fight nor march.[62] Amongst the lost arts, still known it would seem to the Chinese, is that of rendering salubrious the site of vast cities and camps. If I am right in the principles I have endeavoured to establish throughout this Essay, this art must have been based on the practical knowledge that, generally speaking, the earth, as framed by nature, is not usually an unhealthy _habitat_ for those races which grow up in her centres of created life, and it is only when man interferes, and interferes imperfectly, that the air and waters become pestilential to him. The secret lies, no doubt, in agriculture, that first of human arts--that art by which civilization exists. That human life is of as much value by the banks of the Meuse, the Scheldt, and the Rhine, as in Sussex or Surrey, is due to the industry of the inhabitants of Brabant and the islands of the Rhine. On man in a great measure depends the position which life is to hold in the scale of fate; he may raise it to its maximum or sink it to zero. Centuries, it is true, may elapse before human industry can render the banks of the Senegal, the Maranon, or the Zambeze, a fit abode for civilized European man, but if the European persist in transporting himself to these haunts, he must discover the means to do so in safety, or perish in the attempt. Nature did