"History is never altered you see, it just fits together like a jigsaw. Funny old thing, life, isn't it?" - Douglas Adams, "Restaurant at the End of the Universe"

While history cannot be changed; it's definition evolves as more puzzles get discovered assembled and (in some cases - for good, bad, or otherwise) re-assembled.

Therefore, look at history not as fact but as a forming image -- never quite complete and yet still unchangeable in nature.