History must be learned in pieces. This is partly because we have only pieces of the past - shards, ostraca, palimpsets, crumbling codices with missing pages, newsreel clips, snatches of song, gaces of idols whose bodies have long since turned to dust - which give us glimpses of what has been but never the whole reality. How could they? We cannot encompass the whole reality even of the times in which we live. Human beings never know more than part, as "through a glass darkly"; and all knowledge comes to us in pieces. That said, it is often easier to encompass the past than the present, for it is past; and its pieces may be set aside one another, examined, contrasted, and compared, till one attains an overview.
-Thomas Cahill, Sailing the Wine Dark Sea: Why the Greeks Matter