Final answer:
A Roman guard sleeping on duty would face severe consequences such as brutal discipline or even summary execution, reflective of the Roman military's strict discipline and constant combat readiness.
Step-by-step explanation:
A Roman guard was expected to remain vigilant at all times while on duty, especially during nighttime watch. Falling asleep on guard duty was considered a severe dereliction of one's obligations. The consequence for such an offense could range from brutal discipline to summary execution, where the soldier might be beaten to death by their peers. This was a reflection of the strict military discipline within the Roman legions, where unit cohesion and preparedness for battle were held in the highest regard.
It's important to note that even the elite Praetorian Guard, which was responsible for the protection of the emperor and had better service conditions, including shorter service duration and higher pay, would also face severe consequences for any dereliction of duty. The Roman military system was designed to foster a sense of constant readiness, as soldiers were trained to be combat-ready through constant drills.