[Sidenote:  The inner edge.]

The old German maritime cities of the North Sea and the Baltic were located on rivers from 6 to 60 miles from the open sea, always on the inner edge of the coastal belt.  Though primarily trading towns, linked together once in the sovereign confederacy of the Hanseatic League, they fixed their sites on the last spurs of firm ground running out into the soft, yielding alluvium, which was constantly exposed to inundation.  Land high enough to be above the ever threatening flood of river and storm-driven tide on this flat coast, and solid enough to be built upon, could not be found immediately on the sea.  The slight elevations of sandy “geest” or detrital spurs were limited in area and in time outgrown.  Hence the older part of all these river towns, from Bremen to Koenigsberg, rests upon hills, while in every case the newer and lower part is built on piles or artificially raised ground on the alluvium.[412] So Utrecht, the Ultrajectum of the Romans, selected for its site a long raised spur running out from the solid ground of older and higher land into the water-soaked alluvium of the Netherlands.  It was the most important town of all this region before the arts of civilization began the conquest by dike and ditch of the amphibian coastal belt which now comprises one-fourth of the area and holds one-half the population of the Netherlands.[413] So ancient London marked the solid ground at the inner edge of the tidal flats and desolate marshes which lined the Thames estuary, as the Roman Camulodunum and its successor Colchester on its steep rise or dun overlooked the marshes of the Stour inlet.[414] Farther north about the Wash, which in Roman days extended far inland over an area of fens and tidal channels, Cambridge on the River Cam, Huntingdon and Stamford on the Nen, and Lincoln on the Witham—­all river seaports—­defined the firm inner edge of this wide low coast.  In the same way the landward rim of the tidal waters and salt marshes of the Humber inlet was described by a semicircle of British and Roman towns—­Doncaster, Castleford, Todcaster, and York.[415] On the flat or rolling West African coastland, which lines the long shores of the Gulf of Guinea with a band 30 to 100 miles wide, the sandy, swampy tracts immediately on the sea are often left uninhabited; native population is distributed most frequently at the limit of deep water, and here at head of ship-navigation the trading towns are found.[416]

[Sidenote:  Inner edge as head of sea navigation.]

While, on low coasts at any rate, the inner edge tends to mark the limit of settlement advancing from the interior, as the head of sea navigation on river and inlet it has also been the goal of immigrant settlers from oversea lands.  The history of modern maritime colonization, especially in America, shows that the aim of regular colonists, as opposed to mere traders, has been to penetrate as far as possible into the land