Wizards used Amplifying Charms. On the Pomona, Georgiana had seen the navy relay orders using cumbersome devices like megaphones. The army obviously could not carry anything so heavy, so they used all kinds of instruments—drums, horns, and trumpets. In fierce battle, these did more than convey orders; their sonorous rhythms also raised morale. In daily military life, they were used for reveille, lights-out, hunting, salutes, and more.
These were only suitable for short-distance transmission. In theory, every light cavalryman carried a saber, but a general's aide-de-camp was not issued one as part of his standard uniform. Instead, he carried a "mailbox." Though many people had scrambled to become Napoleon's aides after he became First Consul, an aide's main duty was actually to carry urgent dispatches—whether on the battlefield, on long-distance missions through enemy territory, or weaving between two armies exchanging artillery fire or two cavalry charges. These aides were all experienced soldiers, holding at least the rank of lieutenant.
Napoleon liked them not because they were professional messengers. Most of them were sons of nobles from the old era, striving for honor and doing their utmost to fulfill their duties. An aide named Marbot had once made a round trip between Paris and Strasbourg within forty-eight hours. One of Davout's aides had covered one hundred and seventy kilometers through enemy territory in nineteen hours without changing horses.
These isolated messengers ran enormous risks, and their "attrition" was high. It was said that more than a hundred messengers had been captured or killed, making high-quality information transmission exceedingly costly.
Using cannon fire to convey messages was suitable for short and medium distances, like arranging a code with someone else: three short knocks on a door, then one long one.
At Mantua, the original signal was four evenly spaced alarm shots, fired