Ghost stories play a very subordinate part in classical literature, as is only to be expected. The religion of the hard-headed, practical Roman was essentially formal, and consisted largely in the exact performance of an elaborate ritual. His relations with the dead were regulated with a care that might satisfy the most litigious of ghosts, and once a man had carried out his part of the bargain, he did not trouble his head further about his deceased ancestors, so long as he felt that they, in their turn, were not neglecting his interests. Yet the average man in Rome was glad to free himself from burdensome and expensive duties towards the dead that had come down to him from past generations, and the ingenuity of the lawyers soon devised a system of sham sales by which this could be successfully and honourably accomplished.[25] Greek religion, it is true, found expression to a large extent in mythology; but the sanity of the Greek genius in its best days kept it free from excessive superstition. Not till the invasion of the West by the cults of the East do we find ghosts and spirits at all common in literature. The belief in apparitions existed, however, at all times, even among educated people. The younger Pliny, for instance, writes to ask his friend Sura for his opinion as to whether ghosts have a real existence, with a form of their own, and are of divine origin, or whether they are merely empty air, owing their definite shape to our superstitious fears. We must not forget that Suetonius, whose superstition has become proverbial, was a friend of Pliny, and wrote to him on one occasion, begging him to procure the postponement of a case in which he was engaged, as he had been frightened by a dream. Though Pliny certainly did not possess his friend's amazing credulity, he takes the request with becoming seriousness, and promises to do his best; but he adds that the real question is whether Suetonius's dreams are usually true or not. He then relates how he himself once had a vision of his mother-in-law, of all people, appearing to him and begging him to abandon a case he had undertaken. In spite of this awful warning he persevered, however, and it was well that he did so, for the case proved the beginning of his successful career at the Bar.[26] His uncle, the elder Pliny, seems to have placed more faith in his dreams, and wrote his account of the German wars entirely because he dreamt that Drusus appeared to him and implored him to preserve his name from oblivion.[27]