Roman camp - units of measure used by Polybios

[D B Campbell]

Why this one, and not the 0,296mm foot?

I believe Dobson has got himself into a bit of circular reasoning here, but I may be wrong.

He seems to say that Polybius' description of the commander's tent (praetorium) must be in Hellenistic feet (which he quotes as 0,355mm) because Polybius uses a measurement called the tetraplethron. (I don't think I've come across such a large "foot" before -- can anyone corroborate this measurement?)

However, tetraplethron simply means 4 plethra, a measure of 100 Greek feet. Why could Polybius not have used the Attic foot of 0,296mm? And thus his measurements would have satisfied his Roman readers.

Later, Dobson seems to be struck by the fact that 120 Roman feet = 100 "Hellenistic" feet. And multiples of 120 are common in Roman measurement (e.g. the actus quadratus being 35.5m x 35.5m, which would be 100 of Dobson's "Hellenistic" feet square). So his "Hellenistic" measurements would tally with standard Roman practice. I think.

Maybe I have missed a crucial step in his argument? :|