The Spanish coastline exhibits a straight and rectilinear trend when compared to the coastal fringe of other European countries, such as Denmark or Greece. Cliffs are well developed in the Spanish archipelagos, e.g. the Canary and Balearic Islands. Along most of the Spanish coast, storm surges associated with a return period of 20 years, range from 0.40 m to 0.90 m. Surges in the Canary Islands associated with the aforementioned return period, show values from 0.25 to 0.30 m. many harbours and coastal cities developed along the Spanish coast, good examples being harbours built inside natural bays, rivers or river mouths and estuarine areas. In the first millennium BC, the Phoenicians started to colonize the Spanish Mediterranean coast, establishing important settlements at Malaga, Almunécar, Adra and Ibiza. The kingdom of Castile promoted harbour construction in the Northern and Southern Spanish littoral.