r still conquered them with
the sword. All through the succeeding centuries the ambitions of kings
in France, or of emperors upon the Rhine, were checked or satisfied in
that natural avenue of advance. Charlemagne's frontier palace and
military centre facing the Pagans was rather at Aix than at Treves or
Metz; and though the Irish missionaries, who brought letters and the
arts and the customs of reasonable men to the Germans, worked rather
from the south, the later forced conversion of the Saxons, which
determined the entry of the German tribes as a whole into Christendom,
was a stroke struck northwards from the Belgian Plain. Caesar's
adventurous crossing of the Rhine was a northern crossing. The
Capetian monarchy was saved on its eastern front at Bouvines, in that
same territory. The Austro-Spanish advance came down from it, to be
checked at St. Quentin. Louis XIV.'s main struggle for power upon the
marches of his kingdom concentrated here. The first great check to it
was Marlborough's campaign upon the Meuse; the last battle was within
sound of Mons, at Malplaquet. The final decision, as it was
hoped--the defeat of Napoleon at Waterloo--again showed what this
territory meant in the military history of the West. It was following
upon this decision that Europe, in the great settlement, decided to
curb the chaos of future war by solemnly neutralizing the Belgian
Plain for ever; and to that pact a seal was set not only by the French
and the British, but also by the Prussian Government, with what
results we know.

The entries into this plain are very clearly defined by natural
limits. It is barred a few hours' march beyond the German frontier by
the broad and deep river Meuse, which here runs from the rough and
difficult Ardennes country up to the Dutch frontier. The whole passage
is no more than twelve miles across, and at the corner of it, where
the Meuse bends, is the fortress of Liege. West of this fortress the
upper reaches of the river run, roughly east and west upon Namur, and
after Namur turn south again, passing through a very deep ravine that
extends roughly from the French town of Mezieres to Namur through the
Ardennes country. The Belgian Plain is therefore like a bottle with a
narrow neck, a bottle defined by the Dutch frontier and the Middle
Meuse on either side, and a neck extending only from the Ardennes
country to the Dutch frontier, with the fortress of Liege barring the
way. Now the main blow was to be