Here’s the Pliny quote:
The eagle was assigned to the Roman legions as their special badge by Gaius Marius in his second consulship. Even previously it had been their first badge, with four others, wolves, minotaurs, horses and boars going in front of the respective ranks; but a few years before the custom had come in of carrying the eagles alone into action, the rest being left behind in camp. Marius discarded them altogether. Thenceforward it was noticed that there was scarcely ever a legion’s winter camp without a pair of eagles being in the neighbourhood.
Horses, Wolves, Boars are all featured on the Republican coin series. Not so much, minotaurs … It’s not really an argument, but surely something went wrong in Pliny’s account or the manuscript or something… Very strange. But then there is the Festus to back it up…
MINOTAURUS. The figure of the Minotaur was among the military insignia, because the projects of the general should not be less mysterious than the labyrinth which held this monster. The Minotaur, it is said, was the fruit of the love of Pasiphae, wife of King Minos, and a bull. But others say that Taurus was just the name of her lover.
A little background on Roman Military Insignia.
Update 8/12/2016: The thing to read on this subject is:
This ‘restoration’ issue of Vespasian takes its inspiration from this republican type (RRC 287/1):
The birds seem to have changed. Crawford calls the ones on the prototype ‘non-descript’ but the birds on the Vespasian aureus seem to be pretty certainly eagles. Did the republican engraver just do a bad job of representing the species or has the Imperial engraver ‘improved’ the type for symbolic reasons. The republican specimens can have some pretty misshapen birds on them:
The literary sources only have woodpeckers associated with the wolf and twins narrative (Ovid, Fasti 3.37 and 54). One type of woodpecker with a crest was known as Mar’s Woodpecker hence the connection (Pliny NH 11.44). But that doesn’t mean other birds aren’t found in art. More than I want to list here. But just as a taster. Here’s an eagle on a glass paste to which we might compare the Ostian Altar:
And another glass paste with a ‘non-descript’ bird on a grape vine (NOT the ficus Ruminalis then):
This last is a pretty common type of image. Sometimes the grape vine has a bird, sometimes not.
Then there are the other republican coins (RRC 39/3 and 235/1) and that mirror we discussed ages ago that should be brought into the discussion but I’ll leave it there for now. Except for just wondering if this weird BM gem with a mysterious head in the scene might not be Roma’s head, like a reverse scaling of the Roma plus wolf-and-twins motif above:
Update 2/5/2014: The important bibliography on this is
A. Dardenay, Les intailles républicaines figurant la louve romaine: essai d’identification des modèles iconographiques. Pallas 76, 2008, 101-113.
Of course, I had this on file the whole time but didn’t remember the relevance until today….