For a more in-depth look, check out ‘The Complete Roman Army’ by Adrian Goldsworthy. It gives a really thorough breakdown of the Roman military's evolution. The Roman military wasn’t static, so it’s important to see how tactics and organization adapted over centuries in response to different conflicts and challenges including the rise of mobile enemy forces.

Don't forget the auxiliaries! Rome didn't just rely on its legions. As they conquered new peoples, they adopted a bunch of their tactics and even units. Cavalry, archers, you name it. All of these auxiliaries would've influenced Roman tactics over time, especially on the frontiers.

The evolution of Roman military tactics is fascinating and complex, reflecting various factors including socioeconomic changes, external military threats, and internal politics. During the early Republic, the manipular legion, subdivided into maniple units of 120 soldiers, offered flexibility and proved effective against the phalanx formations of their adversaries. However, as Rome's territorial holdings expanded, warfare became more protracted, requiring troops capable of long-term campaigns far from home.

By the late Republic and early Empire, armies became increasingly professional rather than levies of citizen soldiers. The Marian Reforms abolished the property requirements for military service, allowing the recruitment of a landless proletariat who could be equipped at state expense. This change facilitated the transition toward the cohort-based organization of the legions, with each cohort consisting of approximately 480 men, and later subdivided into centuries.

Tactically, the cohort system was better adapted to the defensive strategies required to maintain a sprawling empire. It allowed for greater command and control, centralization of legionary strength, and improved logistical coordination. Outside influences, such as encounters with mobile cavalry forces on the eastern frontiers, prompted Roman adaptations including the integration of auxiliary forces and horse archers.

Over time, the heavy infantry legions that had been the backbone of the Roman military machine gave way to a more diverse force composition in response to varied threats. We must remember that tactics never evolve in isolation but alongside changes in military technology, training, leadership, and the ever-present need to adapt to the enemy's own evolutions in warfare.

lol the only tactic Rome needed was to show up and people surrendered. too bad they forgot how to do even that after a while.

Doesn't the shift from maniples to cohorts also have to do with how the Romans supplied their armies? Like, it must've been way harder to supply all these smaller units once you're operating over huge distances in the later empire?

I think a big thing to consider is how the Roman military was a reflection of their society and politics. In the early Republic, soldiers were essentially citizen-farmers, right? So tactics were built around this idea of short campaigns close to home. But later, as the empire grew, you needed a professional standing army, which kinda necessitated those tactical shifts you're talking about.

The manipular formation was rad because it was super flexible, right? It allowed the Romans to maneuver units separately in battle which was a gamechanger compared to the Greek phalanx. But then as the Empire expanded, they needed a more robust system so switch to cohort structure which was like bigger tactical units instead of the smaller maniples. easier to manage on the big picture scale imo.