This was a legion of Christian soldiers from Thebes serving under the Romans in Gaul under Maximian. They refused to join in the Roman Gods for Victory sacrifices and were consequently decimated.
Decimation was a Roman specialty which involved killing every tenth man to make the rest see sense. And, if they still refused, every tenth man from those remaining. And so on, until they gave in.
But the legion of thousands stood fast until the last ten men — who went off in a job lot. The legion was obliterated. The Celtics in Gaul must have laughed their socks off (if they wore such things) to see such Roman folly.
Our Saint is for some strange reason the Patron of North Austria, where there is an abbey in his name with a tradition of an unbroken chant. Is it still going on? If so what do they chant — is it like an everlasting football song?