I always thought Caesar's real name was Reginald Kennith Dwight... or Salmon Rushdie...
All joking aside, some excellent points about the Legion's infrastructure have been brought up.
As for the Romans and their colonization techniques, the game is far off from the truth (but then, that's expected, because the in-game Caesar doesn't exactly have a replete library of classical documents at his disposal).
While the Romans were especially brutal towards the Gauls, Germanic Tribes, and Britons, they did not brutalize societies they viewed as civilized as much as the societies they viewed as "barbarian".
Case and point: When Julius Caesar invaded Gaul in the first century BC, he did so for reasons both personal and political. While his primary goal was to obtain personal wealth to get himself out of debt from his less-than-reputable political dealings, the Gaulish tribes also posed a particular threat to the Roman Republic on its northern border. For over a century, many Gaulish tribes had been attempting to cross into Italy and take Roman farmland around modern day Venice. Since this land was already taken, and Romans generally despised the barbarians, wars broke out easily. Right before Caesar, they culminated in the Cimbrian Wars, in which populist idol and general Gaius Marius waged a series of decisive battles against the Cimbri and Teutones tribes with the result of hundreds of thousands dead on the barbarian side and minimal casualties on the Roman side. Caesar acted similarly in Gaul. Since the Gaulish people were of little value to Caesar free and their cities were of little value to the Roman people as they were, he decided to assault them, enslave the majority of the Gauls and burn the majority of the cities. Caesar went into an area populated in the range of 4.5 million and reduced the population to about 2.5 million. While he left an awful streak of carnage behind, he also left order, and the opportunity for new, superior cities to be built, for example Lutetia, a highly organized and clean city now known as Paris. Where there was once squalid infighting and illiteracy, the Romans brought sanitation and culture.*
Let's look at that conquest side-by-side with the Roman conquests of Greece and Egypt. The Romans assaulted Greece after the close of the second Punic War. Once Carthage was destroyed, the Romans decided to expand West, mainly because taking such cities as Athens would result in an incredible economic boost. To understand the comparison between mid-Republican Rome and its contemporary Greece, one must understand that the mid-Republican Romans were not the cultured master engineers of the Empire during the Pax Romana. After the conquest of Carthage, the Romans controlled a good bit of the Mediterranean sea; however, their wealth was new-found, and their culture was extremely weak. Greece, conversely just recently saw the conquests of Alexander the Great, whose generals dragged all the riches of the Orient back to the Occident with them. Thanks to both Alexander and previous great leaders, philosophers, architects and the such (for example men like Pericles -who was responsible for building the Acropolis we see in modern Athens-) Greece was already a cultured, rich and great land. The Romans, themselves barbarians at this point, invaded under the command of famous generals like Scipio Africanus and Marcus Marcellus. Unlike in Greece, the Romans here did not burn and enslave everything in sight. Rather, they annexed the already-established and thriving cities of Greece, and took whatever they wanted back to Rome. The result was a new flourishing of Roman culture, based on that of Greece.
Something like this, I would imagine, would happen between Caesar and NCR. The in-game Caesar has already likened New Mexico and Arizona to Gaul, and he has treated the tribes of the area as such. As Tagaziel deduced, Caesar has improved his lands' economy and infrastructure, as well as their general safety, much like the real Caesar in his Gallic Wars. Perhaps, Tucson could be likened to Lutetia for him. I would imagine that the lands of the NCR would be much like Greece, rather than Gaul for the in-game Caesar, because its cities -San Francisco, Shady Sands, Vault City, New Arroyo- are much like the historical Athens and Corinth. While the Romans did assault those historical cities and did plunder them, they did not massacre all the Greeks, but rather allowed them to maintain their culture and flourish. Likewise, I would imagine the in-game Caesar would allow these in-game NCR cultures to flourish.
I apologize for such a long post, and I am sure that all that I just wrote was already known by some. Please know that I am not trying to lord knowledge over people, just let those who don't know in on it in a relatively abridged fashion. Like I said, I'm not assuming everybody here doesn't know this stuff, it's just that ancient history is my academic passion.
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* The Gaulish tribes already had complex socities before the Romans; however, the societies were marred by a lack of real architecture, engineering, or written language. These three things allowed in part allowed the barbarian Gauls to turn into the ultra-cultured French.