In its narrower sense, Thessaly is the valley of the Peneus, which is said, in Herodotus, to have once been one continuous lake, but afterwards discharged its waters into the sea by breaking through the heights between Ossa and Olympus. This clearly shews that the tradition applies to the valley of the Peneus alone, for the valley south of mount Othrys, for example, could not have been inundated, whereas the fertile plains of Pherae about lake Boebeis as far as the Pagasaean gulf, from which it is separated only by a few hills, may very easily have been inundated. The statement, therefore, is evidently correct; its truth may even now be seen, and the ancients judged correctly. However, to refer the draining, which cannot have been the work of human hands, but must have been effected by revolutions of the earth, to the historical ages is a mistake, because we are accustomed to compress the events of many centuries within the small space of our historical knowledge. The opposite mistake consists in assuming, within the sphere of history, longer intervals than really exist. The duration of a century seems to be very short, but if we examine it more minutely, it is a long period for historical changes. If, for example, we look at Germany and our ancestors 150 or 160 years ago, how different do we find them from ourselves in their mode of living, in their ideas, their occupations, and maxims, and that too in the highest as well as in the lowest classes of society! People have imagined that Rome, from the time of Servius Tullius to that of Cicero, remained in its forms essentially the same; but this is quite impossible, and the difference must have been enormous. Even when we look at nations which seem to admit of no change, for example, the Hindoos, great differences are still manifest at different times: life is ever changeable. I do not believe that this remark is superfluous; it is very important to the historian to have it always present before his mind; it is impossible successfully to treat of ancient history without a thorough knowledge of modern history.