It was generally held that if the required cult were not rendered them, they would punish this neglect with wrath, but that they showed their benevolence to those who deserved it by zeal in serving them.[142] The dead were capable, like the living, of gratitude as well as of resentment. The greater had been their power in this world, the more considerable it remained in the other, and the more advantage there was in securing their protection or even their co-operation. Servius reports the existence of the singular belief that souls had to swear to Pluto never to help those they had left behind them on earth to escape from their destiny.[143] Such was, then, the extent of their supposed power. But all the dead were not, like some of the heroes who had become the equals of the gods, capable of performing prodigious deeds. Many, gifted with less force, were concerned with lesser interests; they did no more than protect their family, the domestic hearth and the neighbouring field, and render small daily services. “Farewell, Donata, thou who wast pious and just,” says an epitaph, “guard all thy kin.”[144] The idea that the ancestors become the tutelary spirits of their descendants who were faithful to their duty to them, goes back to the remotest antiquity and probably lies at the foundation of the cult of the Lares.[145] But the field of action of these genii was multiple, since they were a multitude, and their functions underwent a further development when they were considered to be the equivalents of the demons of the Greeks. “The souls of the dead,” Maximus of Tyre[146] tells us, “mingle with all kinds of men, with every destiny, thought and pursuit of man; they support the good, succour the oppressed and punish the criminal.” Plotinus, recalling the universal custom of paying cult to those who have gone, adds: “Many souls which belonged to men do not cease to do good to men when they have left the body. They come to their aid especially in granting them revelations.”[147]