114 Wallenstein
of the wealthy archbishopric of Magdeburg, where the new prince-
bishop was to be none other than Ferdinand’s own twelve-year-old son
Leopold.^18
An Italian entanglement
The Danish peace was formally concluded in July 1629, but how far
from peaceful things were is revealed by Wallenstein’s own figures. He
had, he told Collalto, sent 15,000 men into Poland and 17,000 to the
Netherlands, at least 12,000 were needed to guard against hostile moves
in Brandenburg and Pomerania, while 6000 were tied down around
Magdeburg, which was proving as recalcitrant as Stralsund had been
the previous year. The wider Empire required a large number of garrison
troops, and men were also needed in other places, while the possibility
of a further attack by Bethlen Gabor had always to be kept in mind. He
was already short of troops, and now he was being asked for 14,000 men
for a proposed campaign in Italy.^19
The details of the war which developed there need not concern us,
but the outline is as follows. In December 1627 the duke of Mantua
died, leaving his possessions to his distant but nevertheless closest rela-
tive, the French duke of Nevers. His two separate territories, Mantua
and Montferrat, both adjoined the Spanish duchy of Milan, and these,
together with Savoy and Venice, were the only parts of north Italy not
under Habsburg control. There had been wars over the succession a
decade earlier, in which Savoy, with French support, had opposed Spain,
so that a pro-French duke in Mantua was now highly unwelcome to the
Spanish. An alternative claimant was found, and with the emperor’s help
archaic Imperial procedures were invoked to declare Nevers in breach of
the law, as he had taken possession of his duchy, both parts of which
were Imperial fiefs, before the succession had been formally established.
He was ordered to quit the territories at once, which he did not, so that
a facade of legitimacy was provided for military enforcement.
The Spanish had already sent forces from Milan to seize Casale,
a powerful fortress in Montferrat, but instead of the expected quick vic-
tory a protracted siege followed, lasting throughout 1628. In October
the French Huguenot stronghold of La Rochelle fell, ending a fourteen-
month siege, so that after a long period of internal troubles France was
able to turn to international affairs again. In February 1629, despite
the winter snows, a French army marched over the Alps and relieved
Casale. The Spanish renewed their attack on the fortress in the summer,
at the same time appealing to the emperor for help in return for the