error as to the true direction of the Prussian retreat.

Napoleon, Soult, and all the heads of the French army were convinced that
the Prussian retreat _was_ being made by that eastern road.

As a fact, the Prussians, under the cover of darkness, had retired _not_
east but north.

The defeated army corps, the First, Second, and Third, did not fall back
upon the fresh and unused Fourth Corps; they left it unhampered to march
northward also; and all during the darkness the Prussian forces, as a
whole, were marching in roughly parallel columns upon Wavre and its
neighbourhood.

It was this escape to the north instead of the east that made it possible
for the Prussians to effect their junction with Wellington upon the day of
Waterloo; but it must not be imagined that this supremely fortunate
decision to abandon the field of their defeat at Ligny in a northerly
rather than an easterly direction was at first deliberately conceived by
the Prussians with the particular object of effecting a junction with
Wellington later on.

In the first place, the Prussians had no idea what line Wellington's
retreat would take. They knew that he was particularly anxious about his
communications with the sea, and quite as likely to move westward as
northward when Napoleon should come against him.

The full historical truth, accurately stated, cannot be put into the
formula, "The Prussians retreated northward in order to be able to join
Wellington two days later at Waterloo." To state it so would be to read
history backwards, and to presuppose in the Prussian staff a knowledge of
the future. The true formula is rather as follows:--"The Prussians retired
northward, and not eastward, because the incompleteness of their defeat
permitted them to do so, and thus at once to avoid the waste of their
Fourth Army Corps and to gain positions where they would be able, if
necessity arose, to get news of what had happened to Wellington."

In other words, to retreat northwards, though the decision to do so
depended only upon considerations of the most general kind, was wise
strategy, and the opportunity for that piece of strategy was seized; but
the retreat northwards was not undertaken with the specific object of at
once rejoining Wellington.

It must further be pointed out that this retreat northwards, though it
abandoned the fixed line of communications leading through Namur and Liege
to Aix la Chapelle, would pick up in a very few miles another