The opening of the sixteenth century marks the commencement of one of the great transitional eras of history, and its changes were not in one direction only. Men's horizon on the physical earth had been suddenly widened by the discovery of a new world; their mental horizon by the re-discovery of an old one, in the revival of letters consequent on the fall of Constantinople and the invention of printing. An intellectual eagerness and a trust in the unbounded possibilities of the future had taken possession of their minds and they were not likely to be satisfied with such a present as they saw around them.