The Baltic, like the much larger Mediterranean,1 of which it is in many ways northern Europe’s equivalent,2 is almost an inland sea. Access to the world’s oceans is provided only by three narrow outlets: the Sound between the most easterly and largest Danish island of Zealand (Sjælland) and the southernmost part of the west coast of what is now Sweden, only 5 km wide at its northern end; the Great Belt between Zealand and the second largest Danish island of Fyn;3 and the Little Belt between Fyn and the Danish mainland (Jutland or Jylland). The Mediterranean is divided into western and eastern basins between Sicily and Tunisia. The Baltic is similarly divided into two well-defined main areas: a larger southern basin between the Danish islands and the coasts of ‘Balticum’;4 and a smaller northern arm-the Gulf of Bothnia. These are separated from each other by an almost continuous string of islands between the Swedish capital of Stockholm and the ancient Finnish capital of Turku (Åbo),5 of which the Åland islands (now Finnish) form the central core.