Polybius knew the army was the key, all right. He had spent years in Roman army camps as guest of his distinguished friend Scipio Aemilianus, watching how everything was done, admiring army organization and discipline, taking notes for his book.
Reenactment of a Roman army camp (Creative Commons Attribution 2.0 Generic license photo by Portable Antiquities Scheme)
The army was the basis of Roman life: you could almost say Rome was like its army. The army was school for the Romans—it was where everything was taught, and every man had to attend. To become a magistrate, a leader, you had to serve a minimum of eleven years in arms. Everyone was a soldier first and THEN a civilian around town. The virtues people looked for in a man were military virtues. How had he behaved as a soldier? What was he like out there on the battlefield?
The Roman Camp, after Polybius (Creative Commons Attribuzione-Condividi allo stesso modo 3.0 Unported license photo by Mediatus)
The army camp was a marvel of organization and discipline. It was laid out like a modern city, with broad avenues and side-streets and square city blocks. There were city gates and high walls with palisades. All around it was a deep ditch. This model of a camp was the same always and everywhere: it didn’t depend on the terrain. It was a perfect fortress, so why not carry it around? Polybius thought that was novel and wise. The Greeks always laid out their camps with the aim of taking advantage of the natural defences of the site: its high ground, rocks, river, woods. As a result its shape was different with each new site. The wiser Romans considered that there were greater advantages to pitching the same camp everywhere. That way the men would know by long habit how to proceed. They would not get in each other’s way and they would feel at home and secure in their new camp, no matter where it lay. Greek soldiers needed instructions every time they were about to pitch a new camp, which caused confusion and delay.
Each afternoon when the Roman army was on the march, the tribunes would ride ahead to look for a spot to pitch the new camp. When they found one, they marked it off with flags. The first, a white flag, was where the consul’s tent would stand. Red flags showed where other well-known “streets” and “neighborhoods” would rise. So when the army showed up, each soldier set right to work. No one needed to hear an order. It was all routine.
Remember: a camp wasn’t only a concentration of foot-soldiers. It was home to cavalry too, with its horses and fodder. All the food and baggage and wagons that an army needs—booty too, sometimes, including a catch of sheep or cattle: it all had to be kept safe and made room for. A camp could easily become a terrible confusion: there was always a danger that men and animals would get in each other’s way. Roman planning had reduced or eliminated that danger. The camp always had the same layout but it could be enlarged. Two armies camped together simply meant two identical camps back to back.
See How Rome Conquered the World (Part 4) and read about the grisly Roman army discipline