Rome stands at the center of the poem. The city's founding, and the empire that will grow from it, is the endpoint of Aeneas's fate. Once Aeneas learns of Rome explicitly in Anchises's descriptions of it in the Underworld, the city comes to symbolize for him the pinnacle of his eventual achievement, spurring him on through all of his subsequent trials and tribulations. For Aeneas and his people, Rome also stands as an embodiment of a new home to replace the one they lost in Troy, a place where he and his people can build a community, can worship their gods, can play out their fate. In short, a home is the source of identity, the place where they can build all the things that are worth being pious to.
At the same time, the Aeneid holds up Aeneas as a justification of Rome's greatness. Virgil wrote the poem during the "Golden Age" of Rome, and the poem stands as a founding myth that both connects Rome to the ancient Greek tradition of the Odyssey and the Iliad, and, by showing how Roman is founded on the values of piety and just leadership exemplified by Aeneas, explains how Rome surpasses that tradition. In the Underworld, Anchises goes so far as to explain Rome's superiority to the Greeks and all other nations. He explains that Rome has the unique capacity to spare the conquered and overcome the arrogant. In other words, Rome's greatest virtue is the ability not just to conquer new territories, but also to make them a part of the peaceful whole. And Anchises is right! Rome really was exceptional for that very reason. Rome managed to conquer much of the known world, including all the lands surrounding the Mediterranean Sea, and sustained two hundred years of peace, a feat that no other civilization since has ever matched.