The Inheritance of Rome: A History of Europe from 400 to 1000,  by Chris Wickham; Penguin, 2009, 720 pages, $29.95. The barbarians who pushed through the gates into the Roman empire were not all bad, but neither were they all good. This is the sober-sided conclusion of this latest attempt at a “definitive” history of what is best known as the “Dark Ages”, the six centuries from the collapse of the Roman empire of the west early in the fifth century AD through to the eleventh century. Wickham says the old “catastrophist” historian’s reading of the “barbarian” conquest began to…