This series of fortified places forms the center of the system of
fortifications against Germany. In a southeasterly direction from it the
Vistula offers another strong natural line of defense strengthened still
more by the two big fortresses of Warsaw and Ivangorod, behind which, on
a bend of the Bug River and almost equally distant from both,
Brest-Litovsk, at the very western end of the vast Pripet swamps,
defends the entrance to central Russia, to Smolensk and Moscow.

Adjoining Osowiec on the north and making even more formidable and
naturally very strong defensive line of the River Niemen are Grodno,
Olita, and Kovno.

The second purpose of all these fortified places is to protect the rear
of an offensive army advancing toward Germany and to offer a haven of
refuge if it should become necessary for such an army to fall back. At
the same time they serve as powerful bases and screens behind which an
army of defense could quickly be changed into one of offense. Not only
had they served well this last purpose at the time of mobilization, but
again and again later on weakened Russian armies succeeded in retreating
behind these protecting shields, from which they emerged again a little
later, bent on new attacks, after they had been strengthened by
reenforcements from Russia's inexhaustible resources of men.

It was thus that the Russian armies saved themselves after Von
Hindenburg's smashing victory at Tannenburg. Out of about 650,000 men,
forming the Army of the Narew, and the Vilna Army, more than 300,000 had
succeeded in reaching the shelter of their fortresses.

At that time the German forces, sadly in need of rest, were much too
small and too weak to attempt an energetic general attack against either
the Niemen or the Narew-Bug lines of defenses. However, in order to
prevent another invasion of East Prussia something had to be done. They
therefore advanced a goodly distance into the province of Suwalki,
occupying even the seat of its government, a town of the same name.
Farther south Osowiec represented a continuous danger to East Prussia,
being very close to the border and on the direct railroad to Lyck.
Though the Germans were in no condition to undertake a siege, they
determined to attempt at least to close the crossing of the Bober at
this most advantageous point.

September 18, 1914, saw the beginning of this movement and ten days
later heavy artillery in limited force was thundering against the gates
of