It is well known that a great deal of information has been preserved in the sacred writings concerning the early fortunes of the human race. From these materials have been compiled what has been called an _Historia Antediluviana_, sometimes considered as forming a separate division of history. What has been said above will satisfactorily account for the omission of this portion of history in the present work; although none can deny the high importance of such traditions in the investigation of the origin, dispersion, and civilization of the human race. 4. The sources of history may be ranged under sources of two general heads; _oral traditions_, and _written documents_ of various kinds. The history of every nation usually commences with oral tradition, which remains the only source, until the art of writing becomes known, and in some degree adopted by the people. 5. Under the name of _traditional history_ or _mythology_, is comprehended all the general collection of oral traditions preserved by a nation; and some such traditional history or mythology is to be found among every people in the first stage of their existence as a community. This mythology, however, is by no means confined to events strictly historical, but embraces every branch of information which may appear to a nation in its infancy, of sufficient importance to be preserved and handed down to posterity. Hence the mythology of a people is invariably composed of very heterogeneous materials; it not only preserves the remembrance of various kinds of historical facts, but likewise the pervading ideas of the people with respect to the nature and worship of their deities; as well as the notions they had formed from observations and experience respecting astronomy, morals, the arts, etc. All these are handed down in the form of historical narrative; because man, as yet unpractised in abstract thinking, necessarily represents every thing to his mind under the figure of some physical object. It is just as useless, therefore, to attempt to mould the mythology of any people into a consistent and connected whole, or indeed into any scientific system whatsoever, as it is difficult to draw a strict line between what belongs to mythology, and what to pure history. It follows, therefore, that mythology should be employed by the historian with great caution; and not without judicious criticism, and an accurate knowledge of antiquity. These correct views of mythology,--the key to the whole of earlier antiquity,--were first set forth and illustrated by Heyne, in his commentaries upon Virgil and other poets, in his edition of Apollodorus, and in various essays published in the Transactions of the Gottingen Scientific Society. It is principally to the aid of these that the Germans owe their superiority over other nations in the science of antiquity.