Willem Jansz. Blaeu is one of the greatest Dutch cartographers of all time. It is little known that he began his production of atlases by publishing those of the sea. His first work was the ‘Het Licht der Zee-Vaert’, 1608. Jan Jansson entered the market in 1620 by publishing a rival atlas and in response Blaeu published the ‘Zeespiegel’ or ‘The Sea – Beacon’, in 1623. It was a greatly expanded atlas with maps at a larger scale than before. A very rare chart of the North Sea displaying the coastlines of England, Scotland, the Low Countries, Denmark and Norway. The chart is paginated ’31’ in the lower right corner and is unfolded with very generous margins. This indicates that the example is from the ‘Groote Zee-spiegel’ which was a larger format issue of the atlas in 1655 which enabled the charts to be bound unfolded. Ginsberg ‘Sea Charts of Norway 1585-1812’ p. 44 2B:16, illust. p. 47; Koeman (1967-70) IV M.Bl 28 no. 32 pp. 78-84, 102.