g all this time, the Austrian General Staff was quietly
preparing for another grand drive through Serbia. It was then that the
150,000 reserve, previously mentioned, was assigned to General
Potiorek's disposal, while his first line was also materially
strengthened.

Nor did the third invasion begin with any dramatic effort. The pressure
was applied gradually, little by little, until the Serbs were finally
face to face with the necessity of shortening their lines, if they were
not to be broken through. Other causes besides the increasing pressure
from the Austrians contributed to the general causes.

Winter was coming on in earnest now. The low bottom lands in the Matchva
Plain were becoming waterlogged; it was impossible to keep the trenches
from filling. The Serbians had, in the first place, made a mistake in
attempting to hold these Matchva levels. On such battle grounds, the
Magyars, from their own level plains, were too nearly their equals. On
level ground, too, the defenders have less the advantage, unless they
are in equal number, and the Serbians were everywhere in smaller number.
This inferiority, too, made it less possible for the Serbian soldiers to
obtain periods of rest away from the constant vigilance necessary in the
first line trenches. The result was that they were under a more severe
strain. They were subjected to all the drawbacks of trench warfare at
its worst, without the respite that is usually accorded to men under
these conditions on other fronts. The nerve-racking strain thus imposed
became finally more than ordinary human beings could endure. Small
wonder that the correspondents with the Serbian army reported many cases
of insanity among the men in the trenches.

Finally the order came to withdraw from the Matchva Plain, to the
foothills of the Tzer Mountains and the heights along the right bank of
the Dobrava River. This retreat, made in the face of no specially strong
attack, did not a little to depress the Serbian rank and file. It was
beginning to feel that its strength was sapping away.

It was soon obvious that a more general retirement would now become
necessary. Complete command of the Tzer Mountains could not be attained
without the expenditure of more energy and ammunition than the Serbians
could afford at this time. So a general withdrawal was ordered, along
the whole line. The Austrians, many of them fresh troops, unused to
defeat, followed up in the footsteps of the retreating Se