For an unknown period, embracing, however, many centuries, the prosperity of the kingdom of Saba continued. Then it suddenly declined; a general emigration took place, and the former paradise was transformed into an uninhabited desert. The cause of this great and profound change, involving the desolation of a vast region and the dispersion of an entire people, is hidden in obscurity. The puerile fables which attribute it to a threatened inundation from the rupture of a dike are unworthy of notice. It is probable that this calamity was mainly due to the diversion of the caravan traffic to the channels of the Red Sea, to the abandonment of stations, to the cessation of revenue, and to the consequent dearth of the means of subsistence. Foreign wars or domestic convulsions, which, aided by increasing luxury and subsequent weakness, also contributed to drain the resources and exhaust the population of the kingdom, may have hastened the ultimate catastrophe that is supposed to have occurred during the first century of the Christian era. From this epoch the traditions of the Arabs become more and more confused. Some tribes seem to have emigrated to Mesopotamia, others to have settled in the vicinity of Medina, then called Yathreb, where they intermarried with the Jews already established in that city. We know nothing further of Arabian annals till the promulgation of the faith of Islam began a new chapter in the history of nations. Before the Hegira no date could be fixed with certainty, as there was no chronological system by which to ascertain the year of an historical occurrence, and no public or private records existed to preserve it. But a step beyond the unreliable transmission of past events by tradition were the inscriptions occasionally made upon the shoulder-blades of animals. Not only was the material indispensable to the scribe entirely wanting, but the ability to use it was possessed by only an insignificant number of the people. Among the nomadic Bedouins contempt for literary accomplishments, except that of extemporaneous poetical composition, universally prevailed. Even in the great commercial city of Mecca, at the time of the publication of the Koran, there was but one man who could write. It was not without reason that Mohammed designated the long and obscure period preceding the Hegira, the Age of Ignorance.