I find it fascinating to compare the Greeks and Romans. Their status as the two great political systems of antiquity would suggest more similarities than differences between them, yet they are polar opposites.
If you make a list of adjectives to describe the Greeks, you'll find their antonyms on a list describing the Romans.
Greeks – theoretical, artistic, cultured, philosophical, egalitarian
Romans – practical, imitative, hedonistic, class-oriented.
These two great cultures were not only opposites, but outliers. The Greeks were too theoretical and less practical than they should have been for their own good. For example, their brilliant military formation, the Phalanx, was basically used in the same form without modification for 500 years. The Romans tried the Phalanx for a time, but fairly quickly abandoned it for the maniple, which was more adaptable to uneven terrain. Greek architecture was limited by their inability to devise the construction materials required for large structures. The Romans expanded building practices to a new level and invented concrete along the way.
The Romans, on the other hand, were too practical. Where possible, they stole the ideas of others and advanced them, but displayed less capacity to think theoretically. They stole gods from the Greeks, and modified them to fit their practical view of the world, displaying a disregard for tradition. When being practical mattered, the Romans excelled. They developed a legal system which forms the basis of our law today. Still, their art was weak and showed little creativity.
How do we explain the differences between the Romans and Greeks? As always we go back to geography, which I believe is the single most important factor in the development of human society. We’ve talked at length about Greece and how it was protected from invasion. Its mountain ranges caused a physical separation of its people, which during the dark ages created an incubator for the Polis.
What about the Romans?
Several geographic factors come into play. First of all Rome was inland and had no port. That meant it did not engage in trade (prior to the First Punic War) and was unexposed to new ideas from abroad. Secondly, the geography was relatively flat offering no protection from invasion. Once the Romans broke their Etruscan link, they fought their neighbors on a regular basis to survive, their citizen army proving superior to all adversaries. When the wars ended, the soldiers went back to their farms. Farming and fighting left no time for philosophy.
The social classes of Rome were more strongly differentiated than Athens and there were few leveling forces. The patron/client relationship provided enough support for the plebs to accept their lower status. It wasn’t until the rise of the middle class (Knights) that the class balance was upset and the patricians lost power.