'Britannia' - Romans on TV?

[Nathan Ross]

"King Arthur," a mythical personage, but certainly not a legendary one.

I'm not so sure; 'mythical' seems to connote something that could never have existed, something magical or superhuman. 'Legendary' would be something that could have existed, but probably didn't, and is known only through dubious stories... Although I admit it's a fine line!

In this case it would depend on the type of 'Arthur' - the 'mythical' one who hangs out with wizards, or the 'legendary' one who may have fought the Saxons in the 6th century...

(I'd say both your rodmakers are non-legendary, btw, but there are legends told about them - another distinction!)

However, I think we can agree that the Roman Empire was neither mythical nor legendary.

where do these script writers get so-called "Celtic" nomens from?

Indeed! 'Antedia' seems to be some sort of Dutch brand pharmaceutical... Perhaps they thought that calling their characters Avittoriga or Boduocca or something would lack suitable 'celtic mythology' appeal?