Many people consider the Roman military more important than any other aspect of Roman civilization. Indeed the military was altered enormously under dictator Caesar Augustus, transforming the legions originally made up of untrained civilians to one of seasoned career soldiers.
Originally the legions had been manned by small farmers...[when] hope of restoring the old republic ended [this changed]. The [new] Roman soldier often owned no land and fought primarily for himself and his commander, who could give him land, money, and a good position...
Roman civilization was most widely changed by a developing language—the result of interactions with other lands and peoples through commerce—and the effects on the economy through trade.
Roman trade was the engine that drove the Roman economy of the late Republic and the early Empire.
High-ranking Senate members (and their sons) were strictly limited in the commerce in which they could engage. However the lower orders (e.g., the Equestrian order) could trade more freely. The Roman abacus became popular. The slave trade contributed to the thriving conditions of Roman commerce. Different kinds of merchants (negotiatores, mercatores and "pedlars") were involved in commerce of varying proportions: from the merchants that dealt in bulk and were much like bankers, to the "pedlars" and stall owners, all contributed to healthy and steady growth in the marketplace.
Trade over land and sea brought a great deal to the empire. With this kind of commerce, more trading occurred and a wider selection of goods were made available to Roman families. Rivers were used in land trade; enormous commercial fleets traded across the sea. With the return of these goods and ships came people and ideas of different cultures (including India and China), practices and language. All of these things influenced the face of the empire, altering it in a way completely different than was accomplished primarily by the military or the developing language alone.