For our knowledge of history we are therefore obliged to rely absolutely upon human testimony, in one form or another, the value of such testimony depending principally upon the directness with which it comes to us from the men and the times under consideration. If it reaches us with reasonable directness, and represents a well authenticated means of studying the period in question from the writings or other traces left by that period, it is properly to be included in the great body of materials which we have come to call historical sources. An historical source may be defined as any product of human activity or existence that can be used as direct evidence in the study of man's past life and institutions. A moment's thought will suggest that there are "sources" of numerous and widely differing kinds. Roughly speaking, at least, they fall into two great groups: (1) those in writing and (2) those in some form other than writing. The first group is by far the larger and more important. Foremost in it stand annals, chronicles, and histories, written from time to time all along the line of human history, on the cuneiform tablets of the Assyrians or the parchment rolls of the mediaeval monks, in the polished Latin of a Livy or the sprightly French of a Froissart. Works of pure literature also--epics, lyrics, dramas, essays--because of the light that they often throw upon the times in which they were written, possess a large value of the same general character. Of nearly equal importance is the great class of materials which may be called documentary--laws, charters, formulae, accounts, treaties, and official orders or instructions. These last are obviously of largest value in the study of social customs, land tenures, systems of government, the workings of courts, ecclesiastical organizations, and political agencies--in other words, of _institutions_--just as chronicles and histories are of greatest service in unraveling the _narrative_ side of human affairs. [Sidenote: Sources other than in writing]