The Christians were thus each generation changing more and more, sometimes leaning towards Greek polytheism and sometimes towards Egyptian mysticism. As in each quarrel the most mysterious opinions were thought the most sacred, each generation added new mysteries to its religion; and the progress was rapid, from a practical piety, to a profession of opinions which they did not pretend to understand. During the reigns of Gallus, of AEmilius AEmilianus, and of Valerian (A.D. 251-260), the Alexandrians coined money in the name of each emperor as soon as the news reached Egypt that he had made Italy acknowledge his title. Gallus and his son reigned two years and four months; AEmilianus, who rebelled in Pannonia, reigned three months; and Valerian reigned about six years. Egypt, as a trading country, now suffered severely from the want of order and quiet government; and in particular since the reign of Alexander Severus it had been kept in a fever by rebellions, persecutions, and this unceasing change of rulers. Change brings the fear of change; and this fear checks trade, throws the labourer out of employment, and leaves the poor of the cities without wages and without food. Famine is followed by disease; and Egypt and Alexandria were visited in the reign of Gallus by a dreadful plague, one of those scourges that force themselves on the notice of the historian. It was probably the same disease that in a less frightful form had been not uncommon in that country and in the lower parts of Syria. The physician Aretaeus describes it under the name of ulcers on the tonsils. It seems by the letters of Bishop Dionysius that in Alexandria the population had so much fallen off that the inhabitants between the ages of fourteen and eighty were not more than those between forty and seventy had been formerly, as appeared by old records then existing. The misery that the city had suffered may be measured by its lessened numbers.