Calling all armchair generals! Boudica's Last Stand.

[Owein Walker]

I'm keeping defile, rampart and camp, because SP would want them, and I can't think of a better reason than that.

I'm not entirely sure what you're getting at.  If you're saying that Suetonius built a camp, of course he did; that is what the Romans did.  On the other hand, if you're saying that some translator's use of 'rampart' (which, as John says, is figurative) means that he constructed an artificial barrier on top of an existing feature, you are indulging in supposition that goes far beyond the evidence.  Tacitus is clear; it is the narrowness of the place that provides the protection.  It was narrow enough for Suetonius to be able to block it with his troops and thus leave no space for the enemy to outflank him.  John is right; it is the topography that counts.

Evidence,hmm,if you mean only using the written accounts then that's a restriction I can't apply, and yes, John is right, it is the topography that counts.

SP would choose a site where  he could place his camp on higher ground, very close to the battlefield. It would not be a short march away from the battle for two reasons.

Number 1/ When moving his troops out of the camp to take up their positions, they would be vulnerable to attack.
Number 2/ His camp is not only a shelter for the civilians, but it is also a strong defensive position that he might need  to fall back to.
I also suggest  SP would need to leave some troops to defend the camp if it was some distance away, and he wouldn't want to do that.

Perhaps my choices are military decisions that are not covered by Tacitus or Dio, but their accounts are brief and omit details throughout. 

Of course topography is everything, that's why I place the camp on higher ground with a slope leading to it, that forms a rampart. The whole slope, ditch, bank and camp are one thing, a bit like a Hillfort of the period . It's a simple defence with a rampart.
It is not something new, and that's why it's not mentioned in detail.

Am I indulging far beyond the evidence?  I am sure I read about SP building camps and ditches, in the Atlas mountains, supplies being further defended with ditches and ramparts during the invasion of Britain against mass attacks, even a camp being attacked and both sides digging more trenches, Julius Caesar has even reverted to ditches when he was vastly outnumbered during a siege. I'm sorry if my memory lacks the details, but all that was years ago.

What I am saying is that these defences were part of the battlefields of the period, and for that reason I think SP would use them too.
He chose a position that was clearly defensive, so it makes sense that he would further strengthen his position.