Last night, I caught the tail end of a PBS program about the Romans and Brits going at it during the Boudiccan Rebellion. I'd always thought that the wedge was one 'slice' of a pie. It seems, rather, that it was a series of saw teeth and not necessarily one tooth. Paulinus, greatly out numbered, lined his cohorts up in a straight line in this saw tooth formation across the plain. The Iceni and allies, had wagons at their backs where their families came to watch the battle. The Iceni attacked and the Romans responded with their 'artillery', the scorpio or bellybuster. The Romans then marched forward, at a quick pace in the saw tooth formation, threw their pilum and continued into the Iceni. They marched through and over the Iceni who were hemmed in by their own rear ranks. They trampled to death any Iceni who fell under them. The benefit (to the Romans) of this formation was that the Romans were on the flanks of the Iceni throughout the battle field. The Romans stabbed at the Iceni in their fronts and at their sides. The Iceni retreated right into their own wagons. By this time the Roman cavalry was in action. Between these and the infantry and the fact that the Iceni were hemmed in by their wagons, a great slaughter of all the Iceni came about.
A demonstration of the usage of the scorpio was shown. In design, it is nothing more than a highly mechanized bow, on a horizontal plane, with a rachet to load it. It seems that the bolt was not barbed and could easily pass through the Iceni shield and the warrior behind it. The 'bellybuster' could be fired three times a minute.