Throughout, it was a flow of things of the mind, not a drift of the bodies of men; of culture, not of populations. And the radiation was ever northward, counter to the drift of the migrations which had begun thousands of years before, and which, in part, seem to have continued to crowd southward even during the period of northward spread of civilization. It was much as in Europe fifteen hundred years ago, when Goth and Vandal and Frank and Lombard pounded their way southward into the Roman empire, but the civilization of Rome—writing, learning, money, metallurgy, architecture, Christianity, laws—streamed ever against the human pressure, until the farthest barbarians of the North Sea had become, in some measure, humanized.