While reading Robert Fabbri's excellent "Vespasian" series, I suddenly realised that the Praetorian Guard (who are heavily featured in the books) might well be very overrated as a fighting force. Despite their reputation as an elite unit, there seems to have been no occasion historically when they performed more spectacularly than regular legionaries. Of course, they were certainly good soldiers but I don't feel there is sufficient evidence to conclude that they were the ancient equivalent of Delta Force, either.