THE NIGHT MARCH
With the emperor demanding action, his mercenary army threatening mutiny and the French showing no signs of surrender, Lannoy decided on one last throw of the dice. He reasoned that freeing the trapped garrison would be enough to placate the emperor, at least in the short term, and even if the French occupied Pavia they would not be able to hold the city once Spanish reinforcements, and the imperial treasure ships to pay them, had arrived in the spring.
Having decided on this bolder strategy, Lannoy smuggled a message to the beleaguered garrison. The imperial plan was simple: Lannoy and Frundsberg would lead a surprise attack against the main French army camped in the Mirabello deer park and whilst the besiegers were dealing with this diversionary assault on their rear, De Leyva would break out of Pavia.
With luck De Leyva's men would find themselves outside the city before the French knew what what was happening. They could then join Lannoy's army in an orderly withdrawal to Lodi where both forces could await the arrival of better weather and their pay.
For his plan to be a success, Lannoy needed to march his men through the night to an undefended section of the deer park wall a mile to the north of the French camps. Unfortunately, marching 24,000 men through a moonless winter's night, and breaking down a stretch of fifteen foot high wall wide enough for them all to enter, took much longer than expected so it was dawn by the time the imperial army was ready to attack.