How to sleep in a contubernium

[Robert Vermaat]

If you are guaranteed to have broken sleep every night for a period of days you will begun to degrade, do it for weeks and you start to see health problems and Roman armies could be on campaign for months. Humans need an interrupted nights sleep regularly to keep functioning at their best.

To the contrary. In fact, one single stretch of sleep is a modern invention. Segmented sleep, or twosleep, was the normal thing to do for milennia, until the invetion of street lighting. people still slept for about 8 hours, but they woke up inbetween to read, pray, or even go visit the neighbours. Sexual intercourse was also more popular after the first sleep. By the later 19th century this way of sleeping began to disappear.
http://en.wikipedia.org/wiki/Segmented_sleep
So it's even likely that there were men awake while others slept, or even the whole tent could be busy halfway the night! Difficult for us to understand, the practice died out and we can hardly imagine this.

Your sleep would not only be broken by your time on duty, you would probably also be woken by your tent mates changing over at regular intervals during the night because space in the tent was so tight.

If you're really tired this won't wake you up, is my experience.

Added to that you would have the command control problems of every single tent party providing sentries. The Century officers would also end up with broken sleep every night to supervise their men.

A simple duty roster would take care of that. Each contubernium would know who was to stand guard at what our. Each man would wake the next on duty. Officers who controlled them would of course also have their watch duties, so I don't see their sleep being interrupted either. They don't have to wake up to check up on each change of the guard, that's the job of the officer on duty.

It seems far more likely to me that complete sub-units would provide sentries on a rotational basis so some nights you would be on guard for part of it as a century or cohort and other nights you could get a complete night's rest.

Sure, but that would leave the question as to what unit could guard the whole camp/fort/site? How many men would have to be on guard at any one time?