During any orderly advance, an army proceeding through the Masurian Lakes will strictly confine itself to the great causeways and to the railway.  During any retreat in which it is permitted to observe the same order it will be similarly confined to the only possible issues; but let the retreat be confused, and disaster at once threatens.

A congested column attempting to spread out to the right or to the left will fall into marsh.  Guns which it has attempted to save by the crossing of a ford will sooner or later find mud and be abandoned.  Men will be drowned in the unexpected deeps, transport embedded and lost; and apart from all this vast wastage, the confusion of units will speedily put such a brake upon the whole process of retirement that envelopment by an enemy who knows the district more thoroughly is hardly to be avoided.

It was this character in the dreary south of East Prussia which was the cause of Tannenberg, and as we read the strategical plan of that disaster, we must keep in mind the view so presented of an empty land, thus treacherous with marsh and reed and scrub and stretches of barren flat, which may be heath, or may be a horse’s height and more of slightly covered slime.

The first phase of the business lasts until the 24th of August, beginning with the 7th of that month, and may be very briefly dealt with.

Two Russian armies, numbering altogether perhaps 200,000 men, or at the most a quarter of a million, advanced, the one from the Niemen, the other from the Narew—­that is, the one from the east, the other from the south, into East Prussia.  The Germans had here reserve troops, in what numbers we do not know, but perhaps half the combined numbers of the Russian invasion, or perhaps a little more.  The main shock was taken upon the eastern line of invasion at Gumbinnen; the Germans, defeated there, and threatened by the continued advance of the other army to the west of them, which forbade their retreat westward, fell back in considerable disorder upon Koenigsberg, lost masses of munitions and guns, and were shut up in that fortress.  The defeat at Gumbinnen occupied four days—­from the 16th to the 20th of August.

Meanwhile the Russian army which was advancing from the Narew had struck a single German army corps—­the 20th—­in the neighbourhood of Frankenau.  The Russian superiority in numbers was very great; the German army corps was turned and divided.  Half of it fled westward, abandoning many guns and munitions; the other half fled north-eastward towards Koenigsberg, and the force as a whole disappeared from the field.  The Russians pushed their cavalry westward; Allenstein was taken, and by the 25th of August the most advanced patrols of the Russians had almost reached the Vistula.

The necessity for retaking East Prussia by the Germans was a purely political one.  The vast crowd of refugees flying westward spread panic within the empire.  The personal feeling of the Emperor and of the Prussian aristocracy in the matter of the defeated province was keen.  Had that attempt to retake East Prussia failed, military history would point to it as a capital example of the error of neglecting purely strategical for political considerations.  As a fact, it succeeded beyond all expectation, and its success is known as the German victory of Tannenberg.