Calling all armchair generals! Boudica's Last Stand.

[MonsGraupius]

"Uncertain whether he should choose it as a seat of war".

ibi ambiguus, an illam sedem bello deligeret... (Annals 14.33)

It might be worth thinking about what sedem bello actually refers to here.

'Seat of war' can have two meanings. In the general sense it can just mean a place where the war happens, a 'theatre of operations' or 'scene of action'. Tacitus uses it this way in Histories (3.32), when he has the people of Cremona complain that their "town had twice been the seat of war" - meaning it had been attacked twice.

Lucan, in Pharsalia Book 2, provides a more developed explanation: "Capua was chosen as the seat of war; [Pompeius] resolved to make Capua the base of his chief campaign, and from there to extend and disperse his forces in order to meet the enemy..."

So Suetonius Paulinus could either have thought simply that he would fight a battle in London, or near London (the first meaning), or that he would make London his campaign base, and gather his troops there before sending them out against the rebels, wherever they might be.

Either way, he was not originally intending to evacuate the place immediately, or (I would say) to fortify it as a redoubt, but rather to base himself there and oversee ongoing field operations. It seems likely that he was surprised by the speed of the enemy's advance and the size of their army, and rapidly decided that he would have to seek a better location for his operational headquarters.

I've no idea why you draw a distinction between the place a army is, and the place an army fights. Moreover, we are told that Suetonius delays: "when he prepared to break off delay and fight a battle". Given it took a whole summer to bring the Romans and Caledonians together at Mons Graupius, Romans habitually took a long time. It would not be unreasonable for Suetonius to have delayed till the next year. So, we know Suetonius was sitting somewhere "his seat for war", for some quite considerable time.

So, Suetonius' seat for war " ...from there to extend and disperse his forces in order to meet the enemy...".

Having chosen his "seat for war", Suetonius, then starts sending out patrols and forces, to start reasserting Roman control over an area and to start pushing back against Boudica. Foot soldiers could only travel about 15 miles out and back in a day, cavalry about 30miles. However, with the use of additional fortifications, he could start controlling an area up to 60miles around his "seat for war". So, long as that area protects his supply lines, he and his troops are then able to live quite happily preparing the army and equipment for war.

However, it is clear to me, that Suetonius was under pressure to "stop delaying" and to go out and pressure Boudica into a major battle.

At the battle of Mons Graupius, this was achieved by steadily increasing the area of Roman control up toward the heart of the Caledonians around Inverness and the Moray coast. We are even told of the impact hearing the Romans daily constructing the road that slowly and steadily brought them closer and closer to where they could strike the heartland of the Caledonians.

So, we can assume much the same. Once Suetonius sets off from his "seat of war", he then slowly develops his area of control, moving it more and more toward Boudica. Slowly, he regains settlements, subdues the rebels, and maintains the area he already controls firmly under his control. This is not the movement of a "point" ... as in a "join the dots". This is a widely dispersed army that is going out daily from each new encampment, and subduing a large area area around, until it is under Roman control, and then moving on to repeat the same.

Obviously, how long it takes to subdue an area, depends on how friendly it is. So, areas that had formerly been under Roman control before Boudica, would have readily submitted to Suetonius. So, perhaps he could have moved quite swiftly, moving camp every few days.

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The narrative is referring to London and does not move away. Which means they were cut off from crossing the Thames. That is the only reasonable way to interpret it.

No it isn't.  You have to look at the Latin.  The verb in the sentence is 'attinuerat'.  'Attineo' means 'to hold on, hold fast, delay, keep'.  Tacitus is quite clear.  What is holding those left behind is weakness of sex, infirmity of age or the attraction of the place.  There is nothing about being cut off, trapped or being unable to cross the Thames.

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Let's look at in context, which is what is important here

(A) he resolved to save the province at the cost of a single town [London]. (B) Nor did the tears and weeping of the people, as they implored his aid, deter him from giving the signal of departure and receiving into his army all who would go with him. © Those who were chained to the spot by the weakness of their sex, or the infirmity of age, or the attractions of the place, were cut off overwhelmed by the enemy

Here we have a narrative at (A) which is clearly referring to London. So, we can assume that the next sentence (B) also refers to London. So, we can also infer that © refers to London. So, all of this action occurs in London as that is where the Narrative is.

And this is confirmed in the next sentence:

Like ruin fell on the town of Verulamium

Where it makes it clear it was referring to London, when it says the same ruin befell Verulamium.

So, the people who were overwhelmed, were overwhelmed in London, where as was quite clearly said, they could have easily walked across the Bridge over the Thames, unless that Bridge had been destroyed.

So, it follows that the reason they were overwhelmed in London, is because Suetonius goes south over the Thames, destroys the bridge, leaving those who through infirmity etc., had taken too long to get to London, unable to cross and so at the mercy of Boudica when she gets to London.

All this action occurs in London!