Viking-age smiths used the process known as riving to reduce a tree trunk to planks or to other useful articles. Rather than sawing the wood, they split it. As a result, the grain of the wood follows the piece being fabricated, creating a much stronger item than if it had been sawn. It's one of several reasons why thin-hulled Viking ships could withstand the rough seas of the North Atlantic. The process repeatedly splits the log, first into halves, then quarters, then eighths, as seen in the photo.