Nelson's history of the war. Vol. XI., The struggle for the Dvina, and the great invasion of Serbia

90 HISTORY OF THE WAR.

and Domeness was held by the Russian Fleet. This meant that the coast road to Riga on the narrow strip of dry land between the meres and the sea was at the mercy of the Russian warships. Such a state of affairs could not continue once the winter frosts set in. The freezing of the Eastern Baltic is erratic. Usually the Gulf of Bothnia is icebound as early as November, the Gulf of Finland and the Gulf of Riga by the end of December, while Windau is closed for only about three days, and the Dago Islands for twenty-four. But by the beginning of December it might fairly be said that no fleet could operate safely east of Libau. In October, however, there was no such obstruction. Against any German advance during that month the Russians had their right flank securely protected by the sea.

The second defence lay in the nature of the country west of the Dvina. Through Dvinsk ran the great Petrograd line from Vilna by Sventsiany, and at the junction it received the line from Libau by Shavli, and the line from Riga, which followed the right bank of the Dvina. Three main roads also converged at Dvinsk, one from the north following the left bank of the Dvina, one from Novo Alexandrovsk in the south-west, and one from the south through the wide region of lakes and marshes which stretched towards the villages of Widsy and Drysviaty. These roads and railways were carried on embankments and necks of hard ground through a country which was as generally impassable for guns and troops as the lake district of Masurenland.

In the same way Riga and the line of the Dvina south of it were defended by a tangle of natural diffi-