*During the siege of Turin during the all-European Thirty Years War, the pro-Spanish faction of Turin, the "blues," were fighting the pro-French faction, known as the "whites." This was an exceedingly complicated civil war with a lot of long pauses for negotiation, double-dealing and shifting no-go zones. The "Piedmontese Civil War" was pretty typical of a proxy war in a buffer state.
*This siege of the capital, Turin, developed a unique military situation where the Citadel fortress of Turin was held by the Whites, while the town itself was held by the Blues, while a White-friendly French army surrounded Turin and besieged the Blues, and then, as a final concentric weirdness, a pro-Blue Spanish army coming from Milan arrived, and more or less surrounded the French.
Furthermore, every faction was firing cannon at one another while scrabbling for supplies during the siege process of starving each other out. For instance, they diverted the rivers of Turin so that the city's grain-mills wouldn't work.
The Whites outside Turin had to somehow communicate with the Whites inside Turin, so they used hollow cannonballs with letters inside. I had heard about this cannonball story some time ago, but this is the first time that I've ever found documentary evidence. It's in French. I had Google machine-translate it.
*Not only, it seems, were the Turinese forces of Prince Thomas of Savoy firing letters embedded in sand, but they were shipping fresh gunpowder inside those same flying hollow cannonballs. To put gunpowder supplies inside a big red-hot cannonball, that must have been some pretty gutsy military engineering.
"The labor of the siege advanced; the French were tightening each day more closely, while communications with the relief army were entirely intercepted. It was in this circumstance (((some time in June, 1640))) that an engineer of the prince, called Zignone, imagined how to pass letters, by enclosing them in a cannonball filled with sand launched to the Spanish outposts; this method succeeded, and it was often used to throw gunpowder into Turin. As powder was lacking, the garrison was extremely careful of its fire, while that of the besiegers was continual.
"On the 25th, two new batteries began to fire, one from the Monte, the other from the ramparts of the citadel; the city suffered much, and feared the consequences of the siege, and the prince was advised to retire to the camp of the Austrians; but Thomas, foreseeing that his departure would infallibly bring about a speedy capitulation, refused the entreaties made to him, and only occupied himself with the care of prolonging the defense. He made work to dig a new canal, by means of which he carried the waters from the River Dora to its mills...."
