called 'the delight of the human race,' and when the last spasm of resistance had ceased, Titus sent Jewish captives, both male and female, by thousands to the provincial amphitheatres to be devoured by wild beasts or slaughtered as gladiators. Yet from a very early period lines were drawn forming a clear though somewhat arbitrary code of military morals. In Greece a broad distinction was made between wars with Greek States and with Barbarians, the latter being regarded as almost outside the pale of moral consideration. It is a distinction which in reality was not very widely different from that which Christian nations have in practice continually made between wars within the borders of Christendom, and wars with savage or pagan nations. Greek, and perhaps still more Roman, moralists have written much on the just causes of war. Many of them condemn all unjust, aggressive, or even unnecessary wars. Some of them insist on the duty of States always endeavouring by conferences, or even by arbitration, to avert war, and although these precepts, like the corresponding precepts of Christian divines, were often violated, they were certainly not without some influence on affairs. It is probably not too much to say that in this respect Roman wars do not compare unfavourably with those of Christian periods. It is remarkable how large a part of the best Christian works on the ethics of war is based on the precepts of pagan moralists, and although in antiquity as in modern times the real cause of war was often very different from the pretexts, the sense of justice in war was as clearly marked in Roman as in most Christian periods.[27] Great stress was laid upon the duty of a formal declaration of war preceding hostilities. Polybius mentions the reprobation that was attached in Greece to the Ætolians for having neglected this custom. It was universal in Roman times, and during the mediæval period the custom of sending a challenge to the hostile power was carefully observed. In modern times formal declaration of war has fallen greatly into desuetude. The hostilities between England and Spain under Elizabeth, and the invasion of Germany by Gustavus Adolphus, were begun without any such declaration, and there have been numerous instances in later times.[28]