51 THE SILESIAN WARS, 1740-5Frederick reserved the right to go to war only when he saw fit, but he
was very soon overtaken by events: at the end of June Prince Charles
and the Austrian army crossed the Rhine above Germersheim, and
threatened to invade Alsace. On 12 July Frederick sent Louis XV a
firm promise to begin operations, and a month later the leading
Prussian columns crossed the Saxon border on their way to Bohemia.
Frederick did not move only in the interests of maintaining the
European equilibrium or his own safety. For Prussia this was also a
period of real and potential expansion. In May 1744 the principality
of Ostfriesland came to the House of Hohenzollern by way of legiti-
mate inheritance, after the death of the last native ruler. Ostfriesland
was isolated on the North Sea coast, and was of no strategic conse-
quence whatsoever. The same could not be said of the districts of
northern Bohemia which had slipped from Frederick's grasp in 1742.
Four months before the new war broke out, Frederick was already
marking on the map of Bohemia the territories which he desired for
himself. These embraced the circle of Koniggratz, the trans-Elbe
bridgeheads of Pardubitz and Kolin, and all the ground on the near
side of the river as far as Saxony (PC 1390) - a rich and (as Frederick
thought) eminently defensible little empire. (See Map 3, p. 342.)
Frederick's intention for the coming campaign was to make directly
for the Bohemian capital, Prague, seize it, and then establish himself
in western Bohemia before Prince Charles and the Austrian army
could return from the Rhine. Bohemia was still almost completely
undefended, and Frederick assembled provisions to sustain the army
for only a matter of weeks, being sure that the campaign would have
been convincingly won before that time was out.
Frederick assembled the forces for the Bohemian invasion in
three main groups. The 40,000 troops of the royal army were to march
from Berlin, barge through neutral Saxony, and strike up the left bank
of the Elbe against Prague. Inside Bohemia Frederick was to join the
Hereditary Prince Leopold of Anhalt-Dessau, who was coming with
15,000 men from the north-eastern provinces by way of Zittau and the
Iser valley. Field-Marshal Schwerin brought 16,000 further troops
from Silesia by way of Glatz.
The mobilisation was accomplished smoothly and secretly, and
between 12 and 23 August 1744 Frederick and the leading elements of
his army made the passage of unoffending Saxony. Zieten and his
1,300 hussars spearheaded the advance into Bohemia from the border
hills, and then the slower-moving infantry of the three great Prussian
columns assembled around Prague in the first week of September.
Prague was a large city, but weakly fortified, and more than
three-quarters of the total garrison of 18,000 men were made up of