The second period of Greek literature, dating from the times of Alexander, and reaching down to the overthrow of the Greek national independence by the Romans, was, in the natural order of things, an era of learning, of criticism, and of imitation. The writers of this period, therefore, abound with references of all kinds to their predecessors and contemporaries. A second age of literature holds up a mirror of the first. Erudition, amplitude, comprehension, method, labour, take the place of spontaneous effort, and of intuitive taste. Commentators, compilers, and collectors abound; and the writers of such an age seem to perform the functions of _caryatides_ in the temple of learning; as if their only business was to sustain the pediment which chiefly attracts the admiration of spectators. Among writers of this class, therefore, we are to look for a copious harvest of quotations; and in their pages we shall rarely fail to meet with evidence bearing upon any question of the genuineness of an ancient writer. The Romans borrowed everything but energy of character and practical good sense, from the Greeks. Their literature, from the first, was of a derived character; their writers added learning to what might be their native genius; and their works reflect the literature of their masters. Sufficiently ample allusions, therefore, to the most celebrated of the Greek authors, as well as to those of their countrymen, are found scattered throughout the Latin classics. Both the Greek and Latin writers of later ages were well acquainted with the literature of brighter times; and they have left in their works ample means for bringing down the chain of references to the time of the decline of learning in Europe--to that time up to which we have already traced the history of existing manuscripts; so that the two lines of evidence unite about midway between the fifth and the fifteenth centuries. The nature, extent, and validity of the evidence that may be derived from the mutual references of authors, will be best exhibited by a classification of its several kinds under the following heads:--