Before we enter upon these campaigns in the East it is well to survey the countries to be invaded, to review the battle lines and travel in these pages over the fighting ground.

The eastern theatre in the first six months of the war, from August 4, 1914, to February 1, 1915, includes the scenes of the fighting in the historic Balkans and in the Caucasus.  But the eastern front proper is really that region where the Teutonic allies and the Russians opposed each other, forming a fighting line almost a thousand miles long.  It stretches from rugged old Riga on the shores of the Baltic Sea in the far north, down through Poland to the Carpathian Mountains, touching the warm, sunlit hills on the Rumanian frontier.  When the total losses of the Great War are finally counted it will probably be found that here the heaviest fighting has occurred.

This is the longest battle line in the world’s history.  Partly on account of its great length, and partly because of the nature of the country, we see the two gigantic forces in this region locked together in their deadly struggle, swaying back and forth, first one giving way, then the other.  This was especially the case in the northern section, along the German-Russian frontier.

[Illustration:  THE WAR IN THE EAST—­THE RELATION OF THE EASTERN COUNTRIES TO GERMANY]

As we view the armies marshaling along this upper section, along the Baltic shore, southward, including part of East Prussia as well as Baltic Russia, we look upon the ancient abode of the Lithuanians, supposed to be the first of the Slavic tribes to appear in Europe.  Hardly any part of Europe has a more forbidding aspect than this region.  There the armies must pass over a flat, undulating country, almost as low in level as the Baltic, and therefore occupied in large part by marshes and lagoons through which they must struggle.  In all parts the soil is unproductive.  At one time it was a universal forest:  thick, dark, and dank.  A century ago, however, Catherine the Great distributed large areas of this comparatively worthless land among her favorites and courtiers.  In this way a certain percentage was reclaimed, and with the incoming of the sunlight more favorable conditions for human life were established.  Yet even now it is very thinly settled.

Through this region the armies must cross big rivers:  the Oder, Dvina, Warthe, Vistula, Pregel, and Niemen, northward and northeastward.  Just above or eastward of that point, where the German-Russian frontier touches the shore, the Baltic curls into a dent, 100 miles deep, forming the Gulf of Riga.  Near the southern extremity of this gulf, eight miles from the mouth of the Dvina, is the city of Riga, ranking second only to Petrograd in commercial importance as a seaport, and with a population of about 300,000.