The first sailors braved the North Sea and the Baltic in open wooden boats: their aims were varied - to fish, to trade, to conquer and plunder. Without maps or compasses, they steered by the sun or by landmarks on the coast. Nevertheless they discovered Iceland and North America and explored the rivers that flowed through Europe and Russia into the Black Sea. With the Frisians and the Vikings, extensive trade routes, better ships, larger harbours and wealthy coastal towns developed. The pinnacle of these advances was the Hansa, an association of port cities running from Bruges to Riga. In...