Note 729 — Chapter XI · —The Anthropo-Geography Of Rivers

More effective than rivers in the protection which they afford are swamps. Neither solid land nor navigable water, their sluggish, passive surface raises an obstacle of pure inertia to the movements of mankind. Hence they form one of those natural boundaries that segregate. In southern England, Ronmey Marsh, reinforced by the Wealden Forest, fixed the western boundary of the ancient Saxon kingdom of Kent by blocking expansion in that direction, just as the bordering swamps of the Lea and Colne rivers formed the eastern and western boundaries of Middlesex.729 The Fenland of the Wash, which extended in Saxon days from the highland about Lincoln south to Cambridge and Newmarket, served to hem in the Angles of Norfolk and Suffolk on the west, so that the occupation of the interior was left to later bands who entered by the estuaries of the Humber and Forth.730 In northern Germany, the low cross valleys of the Spree, Havel and Netze rivers, bordered by alder swamps, were long a serious obstacle to communication, and therefore became boundaries of districts,731 just as the Bourtanger Moor drew the dividing line between Holland and Hanover.