In the last excerpt, the new trainees are awakened by the sounding of horns, a signal used to great effect and not just to scare the sleep out of trainees at dawn. How did the Roman military communicate, and how effective were those methods?
The main musical instruments we know were used by the Roman military to communicate included the tuba, the cornu, and the buccina. All of these were horns of varying sizes and with different sounds.
The tuba (translated as “trumpet” in many sources) was a straight copper or iron horn with a cone-shaped bell—nothing like the tuba used in modern music, it was more like a trombone if you remove the slide and curves (tuba in Latin comes from tubus, which just means “tube”). Tuba sounds signaled work commands, and were used on the battlefield along with the cornu to transmit orders.
The cornu (often translated as “cornet”) was a very large horn, somewhat similar in shape to a modern tuba, a gigantic curved horn with a bell opening. According to Vegetius, this horn was used “only to regulate the motions of the colors,” which Professor Russell of Penn State interprets to mean that it was used to “direct the movements of soldiers under a certain sign.” What I believe this refers to is that the cornu horn is a signaling device used whenever a legion’s soldiers are moving “under the colors,” or moving as a unit in some kind of official capacity—such as “fall in” to a formation, “march ahead” or “fall back” or other such commands, basically orders to assemble, move, and/or disperse as an entire unit.
The buccina (or “horn”) was similar to the cornu, but smaller and had more of a flare on the bell. This horn appears to have been primarily reserved for signals in camp, such as “change shifts” for the guards, “wake up,” and “meal time.”
Use in combat
Together, the trumpet and cornet appear to have been combined on the battlefield to transmit orders. I have not found any particular references that have any specific calls or sounds that were used, but it seems reasonable to assume that there were specific horn calls—think Morse Code, long blasts and short “toots” used together—and that a specific cornet call first followed by a trumpet call second could be used to signal specific units to do specific things.
How effective were these systems? It would appear that they worked quite well. It certainly seems that if the Roman military at the time Vegetius was writing was still using the same techniques, that they were probably pretty effective.
What about Drums?
One thing that does not appear to have been used by the Roman military is a drum, at least not as a signaling or order transmission tool. The only use of percussion that I have uncovered is the centurion’s use of his vine-stick being tapped against his shield to mark time as the soldiers marched.
Other signaling techniques
Early in the first episode of Rome, on HBO, Vorenus is seen using a whistle to signal the century to perform certain actions. There have been wooden whistles excavated in Roman ruins, but apparently none within any places known to be military in nature. There is an argument that any use of a whistle for such signaling would be confusing, since the centuries in a cohort would not usually be terribly far apart, but I am not convinced that a verbal shout would be sufficiently loud even over the distances involved in issuing orders to a ten-man-abreast formation—one which would likely have been 60′ or more wide—in a pitched battle. If it were, it would be just as much of a problem for voice orders to be heard by the wrong century as it would be to hear whistle blasts, but using a whistle would be faster. So despite there being no direct evidence for it, I think it does make some sense to have a small-unit instrument (such as a small whistle) as a signaling device. There is ample evidence that earlier militaries (the Spartans, in particular) using flutes, and it doesn’t seem much of a stretch to conclude that there might have been something similar on a small unit scale in Roman units.
There is, however, no evidence for it.
When the situation was calmer, orders often appear to have been transmitted face-to-face. Each morning in camp, the centurions—or, at least the most senior centurion in each cohort, the pilus prior—would meet in the tent with the commander to receive the day’s initial orders and then transmit them to the troops directly.
Also, written orders were transmitted occasionally. This would especially be true if orders needed to be sent to widely separated units (such as from Caesar in Cisalpine Gaul to Labienus in the middle of Gaul). Caesar, in fact, had developed a crude encryption system (the Caesarian Cipher, a simple substitution cipher) that enabled him to send encrypted messages.
Being able to accurately and quickly send orders to troops—particularly on an active battlefield—was, and still is, a terrific challenge. Modern radios, satellites, and encryption systems had their roots in the methods ancient militaries developed to solve this problem, including the use of military music as a signaling device.
“Roman Military Brass Instruments” (Daniel A. Russell, Professor of Acoustics & Director of Distance Education, Graduate Program in Acoustics, The Pennsylvania State University) https://www.acs.psu.edu/drussell/Asterix/02-RomanBrass.html (retrieved 12 NOV 2019)
De Re Militari (Vegetius)