THE TRIPLEX ACIES

            The Roman legion was organized into maniples. These were like loose phalanxes. The hastati and principes maniples had 120 men each and the triarii had 60. It is unclear how the men were placed in the hastati and principes maniples. It could have been 10 men across and 12 rows deep or 20 men across and 6 rows deep. Bernard Montgomery suggested that the formation was four rows deep.  6 rows seems the most logical because if the men were rotated to the front in battle to keep them fresh, 12 rows seems too many soldiers waiting a long time to get to the front and 4 seems too little. More than 6 rows was not a good idea since it was the soldiers who were waiting for combat that had a lot of stress. Imagining what was happening in front could be worse than actually being in the thick of it.

The adoption of maniples to replace one big phalanx required a new formation. The Romans decided to place ten maniples apiece in three rows. This was known as the triplex acies.  The formation also allowed men to be relieved without the formation being broken up. While the use of the stabbing sword entailed less exertion than a barbarian would have to use with his long slashing sword, it was still exhausting sticking a sword in bellies and bashing faces with your scutum. Because it was not wise or effective to let the front line do all the work, the centurion had a whistle he would blow when he wanted the front line to drop back and the next line to move up. Some historians are skeptical of them using a whistle blow to exchange rows at regular intervals. The whistle might blow when a legionary was heavily involved with fighting an enemy and could not break away without the warrior following him into the formation. And it seems too robotic for a chaotic battle scenario. It was possible that the relief of the front rankers was done either by the legionary at the front calling for relief from his mate behind or the mate yanking on his uniform to tell him it was time to fall back. When a switch occurred, the front soldier would simply step to his left and funnel back through the other ranks until he was in the back line. Meanwhile the man behind him had taken his place and the fighting continued with little pause. If the entire maniple had been fighting for an extended time, the principes could be ordered forward to replace the hastati maniples. 

            Polybius describes the legion from a bird’s eye as looking like one color on a checkerboard.  This arrangement was called the quincunx. The hastati maniples would make up the front line, but it was not a solid front line. There were gaps between each maniple that were the width of a maniple. The second line was the principes maniples. They were also spaced about a maniple apart, but they covered the gaps in the first line. It was the triarii that maintained a solid front. Their maniples would have looked like three lines of soldiers in the Napoleonic Wars, except they were armed with spears, not muskets.

            Ever since Polybius wrote his history of the Punic Wars, there has been a spirited debate about how the triplex acies fought.  To some military historians, as well as some military tacticians, leaving gaps in your formation is asking for disaster when facing an enemy that fights in no formation at all. Seemingly, a charge by Gauls would hit the hastati, but also flow into the gaps causing the maniples to be double enveloped – one of the worst things that can happen to a unit in battle. Those historians and tacticians have suggested several addendums to Polybius’ description of the formation. They assume he neglected to describe how the formation worked in battle. Surely the Romans did not leave those gaps when the battle began. One suggestion is that since the maniple was already divided into a front and rear century, it would make sense for the rear century to move into the gap to create a continuous line. Another theory was that before the battle began the hastati would spread out even more so that way the gap was covered by the hastati without having to move a century into the gap. This would give them 6 feet of space on each side. That seems a bit too loose to me. A third suggestion is that the principes would simply move up into the gaps before fighting started. However, this would have left the general with no reserves (unless he used the triarii, which was normally the rear guard), so it seems the least likely solution to the gap problem. After many hours pondering this problem and after going back and forth on it, I suggest we trust Polybius. If the triplex acies formed a line with no gaps, he would have mentioned that.  Because he did not, I think it is safe to assume that the legion fought with the gaps. It would not have been disastrous because the principes retained their pila and could counter any infiltration into the gaps. Or move up to catch the enemy in a trap. Keep in mind, that aside from the first two rows which would have been fixated on the enemy in front, the other men on the far right and far left columns could have easily turned to flank enemy that had flowed into the gap to their side. In a sense, the enemy would have moved into a trap with Romans on both sides and in front.  Some historians posit that most of the velites would not have moved through the maniples to reach the area in front of the triarii, but some could have remained in the gaps to gain recognition by protecting the space. These velites wanted the breath of the enemy in their face instead of hurling javelins at him from afar. This type of bravery might result in a promotion to the hastati.