Wellington's command may be found upon
the Brussels road attempting to join the Prussians.

The general plan of what happened upon that decisive 16th is simple
enough.

The left-hand body, under Ney, goes forward up the Brussels road, finds
more resistance than it expected, but on the whole performs its task and
prevents any effective help being given by the western half of the
Allies--Wellington's half--to the eastern half--the Prussian half. But it
only prevents that task with difficulty and at the expense of a tactical
defeat. This action is called Quatre Bras.

Meanwhile, the right-hand body equally accomplishes the elements of its
task, engages the head of the Prussian line and defeats it, with extreme
difficulty, just before dark. This action is called Ligny.

But the minor business conducted by the left, under Ney, is only just
successful, and successful only in the sense that it does, at vast
expense, prevent a junction of Wellington with Blucher. The major business
conducted on the right, by Napoleon himself, in support of Grouchy, is
disappointing. The head of the Prussian line is not destroyed; the
Prussian army, though beaten, is free to retreat in fair order, and almost
in what direction it chooses.

The ultimate result is that Wellington and Blucher do manage to effect
their junction on the day after the morrow of Ligny and Quatre Bras, and
thus defeat Napoleon at Waterloo.

Now, why were both these operations, Quatre Bras and Ligny, incompletely
successful? Partly because there was more resistance along the Brussels
road than Napoleon had expected, and a far larger body of Prussians in
front of him than he had expected either; _but much more because a whole
French army corps, which, had it been in action, could have added a third
to the force of either the right or the left wing, was out of action all
day; and wandered aimlessly over the empty zone which separated Ney from
Grouchy, Quatre Bras from Ligny, the left half of Napoleon's divided army
from its right half_.

This it was which prevented what might have been possible--the thrusting
back of Wellington along the Brussels road, and even perhaps the
disorganisation of his forces. This it was which missed what was otherwise
certainly possible--the total ruin of the Prussian army.

This army corps thus thrown away unused in hours of aimless marching and
countermarching was the First Army Corps. Its commander was Erlon; and the
enormous blunder