[Sidenote:  Swamps as barriers and boundaries.]

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.

[Sidenote:  Swamps as regions of survival.]

Swamp-bordered regions, as areas of natural isolation, guard and keep intact the people which they hold.  Therefore they are regions of survival of race and language.  The scattered islets of the Fens of England furnished an asylum to the early British Celts from Teutonic attacks,[732] and later protected them against dominant infusion of Teutonic blood.  Hence to-day in the Fenland and in the district just to the south we find a darker, shorter people than in the country to the east or west.[733] Similarly the White Russians, occupying the poor, marshy region of uncertain watershed between the sources of the Duna, Dnieper and Volga, have the purest blood of all the eastern Slavs, though this distinction is coupled with poverty and retarded culture,[734] a combination that anthropo-geography often reveals.  Wholly distinct from the Russians and segregated from them by a barrier of swampy forests, we find the Letto-Lithuanians in the Baltic province of Courland, speaking the most primitive form of flectional languages classed as Aryan.  The isolation which preserved their archaic speech, of all European tongues the nearest to the Sanskrit, made them the last European people to accept Christianity.[735] The great race of the Slavic Wends, who once occupied all northern Germany between the Vistula and Elbe, has left only a small and declining remnant of its language in the swampy forests about the sources of the Spree.[736] [See ethnographical map, p. 223.] The band of marshlands stretching through Holland from the shallow Zuyder Zee east to the German frontier, has given to Friesland and the coast islands of Holland a peculiar isolation, which has favored the development and survival of the peculiar Friesian dialect, that speech so nearly allied to Saxon English, and has preserved here the purest type of the tall, blond Teuton among the otherwise mixed stock of the Netherlands.[737]