This is something I didn't know about at all, really, but it turns out that historically the Romans had a really hard time pacifying and then protecting the northern reaches of the province of Macedonia after they destroyed the Macedonian state itself. One of the main troublemakers/freedom fighters/looting loonies was the Scordisci, a decent-sized confederation of Gallic tribes who had settled in Illyria, probably during the same wanderings that produced the Galatians. The Scordisci don't seem to have liked anybody very much, especially the Romans, but then who can blame them for that. They raided, invaded, and incited or paid other people to do the same things. It is possible that Mithridates of Pontus got in on the act and sent them money and materials because he hated the Romans as much as they did. This battle comes in 109 BC, just before his time, but we think it gives a flavour of the kinds of things that were going on.
Here is Gordon's report, somewhat edited, as head honcho of the Scordisci:
No doubt the usual lies have been or are about to be promulgated by the Roman commanders (who are firstly politicians) in respect of their encounters with the Illyrians. What really happened was this.
The Illyrian plan was clearly to deliver a massive blow against the two legions facing their left while fending off the other legions.
In an email exchange, I remarked how tough the Illyrians can be, since their warbands count as higher than usual quality, which meant that their initial charge went home with enhanced ferocity. Gordon replied that this was the case, and also that the Roman flank was relatively unprotected, which was why he was able to get his peltasts into the fight as well. In addition, Simon did a great job of keeping the other legions off the inner flank of the warbands, albeit at the cost of most of his command.
Photos, provided by Gordon: