500 B.c., boat- shaped graves-with tall stones at either end representing prow and stern-were common.
The boats themselves, Hagen notes, were growing sturdier. Around A.D. 600, Norwegians built the first full keel-a single, arched beam, usually oak, which under- girded the hull. Ships now could sur- vive long voyages; Scandinavia had the technology to enter the Viking Age.
Of the many accounts of the Vi- kings' extraordinary outward surge during the ninth, loth, and 11 th cen- turies, the best...