All over the sand and bog district of the north of Germany, crops, mostly of rye and buckwheat, have for centuries been grown _year after year on the same land_, kept productive by marling and peat manure, on what Hanssen describes as the 'one-field system.'[561] This system is found in Westphalia, East Friesland, Oldenburg, North Hanover, Holland, Belgium. Denmark, Brunswick, Saxony, and East Prussia. Over parts of the district under this one-field system the single-farm system prevails, in others the fields are divided into 'Gewanne' and strips, and there is scattered ownership. «in North Germany.» Now, possibly this one-field system, with its marling and peat manure, may have been the system described by Pliny as prevalent in Belgic Britain and Gaul before the Roman conquest, [p373] but certainly it is not the system prevalent in England under Saxon rule. And yet this district where the one-field system is prevalent in Germany is precisely the district from which, according to the common theory, the Anglo-Saxon invaders of Britain came. It is precisely the district of Germany where the three-field system is conspicuously absent. So that although Nasse and Waitz somewhat hastily suggested that the Saxons had introduced the three-field system into England, Hanssen, assuming that the invaders of England came from the north, confidently denies that this was possible. 'The Anglo-Saxons and the Frisians and Low Germans and Jutes who came with them to England cannot [he writes] have brought the three-field system with them into England, because they did not themselves use it at home in North-west Germany and Jutland.' He adds that even in later times the three-field system has never been able to obtain a firm footing in these coast districts.[562] «The three-field system» There remains the question, where on the Continent was prevalent that two-or three-field system analogous to the one most generally prevalent on the manors of England? «in the old Suevic and Roman districts.» The result of the careful inquiries of Hanssen, Landau, and Meitzen seems to be, broadly speaking, this, viz., that setting aside the complication which arises in those districts where there has been a Slavic occupation of German ground and a German re-occupation of Slavic ground,[563] the ancient three-field system, with its _huben_ of scattered strips, was most [p374] generally prevalent south of the Lippe and the Teutoberger Wald, _i.e._ in those districts once occupied by the Suevic tribes located round the Roman _limes_, and still more in those districts within the Roman _limes_ which were once Roman province--the 'Agri Decumates,' Rhætia, and Germania Prima--the present Baden, Wirtemberg, Swabia, and Bavaria, on the German side of the Rhine, and Elsass and the Moselle valley on its Gallic side.[564] These once Roman or partly Romanised districts were undoubtedly its chief home. Sporadically and later, it existed further north but not generally.