Where was the Roman Army in AD408?

[Nathan Ross]

Is there a reference to this that explicitly states 40 guards?

Constantinus Porphyrogenitos, de ceremoniis aulae 1.86.

This is a very late source, of course, and various other types of bodyguard are mentioned in the later centuries - spatharii, excubitores, etc - but the candidati are attested by Ammianus in the mid 4th century. I do wonder whether at that date the word might have been a sort of nickname used as a synonym for those men of the protectores domestici assigned to the emperor's personal protection, though.

Interesting that Olympius, the infamous magister off of Honorius, is described by Zosimus at one point as 'commander of the court guards' - clearly he (or the translator!) means the candidati.