Sub-Roman Britain (Cavalry etc)

[Robert Vermaat]

it seems that the Visigoths were startled by Ecdicius' sudden and safe appearance, and upon knowing that he was son of the Emperor and Magister Militum they retreated for fear that the Imperial army was behind him.

Hardly.
Avitus was probably dead by 456, neutralized by Ricimer, who remained the great power in Italy until 472. No friend of Avitus' son, then.
In fact the Goths probably knew that no imperial army could follow on the heals of Ecdicius, because Euric had just defeated Anthemiolus and his army. Anthemiolus was the son of the emperor Anthemius, who had been sent by the emperor Leo to Italy to challenge Ricimer. With his army defeated and another rival (Olybrius) sent from the East, Anthemius' days were numbered also. Anthemiolus' army was in fact the last officially Roman army ever to set foot in Gaul. By 475, the Roman emperor Nepos officially legalised the loss of Gaul by granting the Auvergne to Euric.

Ecdicius was not named magister militum for another 2 years to come.

So with any posssible support for the Gallic nobles crushed, and with Ricimer as enemy in Italy, the Gallic nobles and Syagrius were on their own. And of course Euric and his Goths were well aware of that.
About the Goths fleeing the scene, I think that Sidonius is putting it on a bit. Poetic license in order to praise a relative.

A rather interesting point which I was trying to get at is that there were likely 200 men in that rearguard, meaning that each man had to have killed ten men and severly injured another who was finnished off by a second member of their band. hock: If Sub-Roman cavalry was as well-led and as powerful as that, then it is plausible that Ambrosius won all his battles with no one but his personal band of cavalry. Take into account that the britons prefered to fight at dawn and at fords, then you have one deadly fighting force, even if it was just 100 men.

One, it's possible that Ecdicius' force contained 19 cavalrymen, plus their retainers. But that's just me guessing.
Two, on what grounds do you base your estimate of a rearguard of 100-200 Goths?