Calling all armchair generals! Boudica's Last Stand.

[MonsGraupius]

So, I hope you will agree, that if you were a rich person from north of the Thames, deciding to take all your valuables over the bridge and head toward Gaul (and Roman-friendly areas of the SE), that you would put whatever pressure you can, to hold or destroy that bridge so that there are no hoards of Iceni flooding over, and so that you can escape.

I will allow you this, ... If your rich person had sufficient influence, they might have engineered the destruction of the bridge, leaving those remaining north of the river at the mercy of the rebels.  This, of course, is entirely irrelevant to the movements and actions of Suetonius.

And this does fit the narrative which is of people being "overwhelmed" in London ... where the bridge is really a draw bridge ...that can be "taken up".

And, I do hope, on reflection, that you will change the "is entirely irrelevant to the movements and actions of Suetonius." because you've already admitted that he would be under political pressure from those escaping south.

We also see, that whether by design or default, the Romans need to hold the area south of the Thames ... because Suetonius will be under political pressure, and it doesn't take an enormous force to hold the Thames defensive line so it is a no brainer that they would. And, with this very small defensive force, Suetonius controls the whole SE of England ... meaning a very small force can secure his supply lines up to the Thames.

And, from that position ... it doesn't matter which way you envisage Suetonius moving ... his obvious supply line is from South of the Thames, so yet again, from a military as well as political viewpoint, Suetonius needs to hold the area south of the Thames.

as a result of this campaign, the use of defensive barriers such as Hadrian's wall and the Antonine wall become the way that the military fight in Britain.

Hadrian's Wall and the Antonine Wall are products of the 2nd century.  Hadrian's Wall was erected 60 years after Boudica's revolt and the Antonine Wall 20 years after that.  They reflect the thinking of their time and have nothing to do with the AD60s.  ld.  It was not a defensive structure to hide behind.  The same applies to the shorter-lived Antonine Wall.

The Antonine wall starts as a line of defensive forts during the Agricolan campaign of 83AD ... which undoubtedly included many who could remember the Boudican campaign. However, it is claimed that the Gask ridge is even earlier (sometime between 70 and 80 AD). Hadrian's Wall was started 40 years after the Agricolan forts. Again within living memory.

From the time of the Thames-Berkshire hill defensive line used by Suetonius, these defensive lines from sea to sea become the normal military thinking in Britain.

DEVELOPMENT OF THE DEFENSIVE LINE IN BRITAIN
Having suggested it was the "normal thinking", does it then fit available evidence? There are two obvious narrowings of Britain at the Wash-Dee line and at the Humber-Ribble line.

If we look at the Wash-Dee line, which would have been the "front line" before Boudica (~50AD), we see that Lincoln is the main fort, toward the east where it is easy to supply from Gaul, but there is no obvious development of a line.

The next narrowing of Britain with a major river is the Humber (If I remember corrected, derives from old English for border). This would have been the "frontline" some time after the Boudican revolt. The major fort here is at York (~71AD), on a major river tributary of the Humber, this is also the most southerly Brigantes settlement as listed by Ptolemy. West of here is a line of forts heading to the river Ribble (Preston).

All later expansion in Britain uses some form of defensive line (Antonine wall, Hadrian's wall, Gask ridge)

I think we can safely say quite conclusively that there is a change toward the defensive line that occurs at the Boudica revolt. As, such, and given the Thames at London, it is undeniable that Suetonius would have used the Thames as a defensive line, and his success with this strategy during the boudican revolt is what changed the thinking toward the use of defensive lines in Britain.