The Aeneid is built in two halves that answer the two Homeric poems. Books one to six are a wandering, an Odyssey: the storm that drives Aeneas to Carthage, his account of Troy's last night and the flight carrying his father and leading his son, the years of false landfalls, the affair with Dido and her suicide when he sails, the funeral games for Anchises, and the descent to the underworld. Books seven to twelve are an Iliad: arrival in Latium, a marriage dispute deliberately inflamed, and a war against Turnus ending in single combat.
Book six carries most of the theological weight. Guided by the Sibyl at Cumae, Aeneas crosses into the land of the dead and passes through its regions, infants and suicides, the fields of mourning where Dido turns away from him without a word, Tartarus, and the blessed groves, to meet his father, who explains a scheme in which souls are purged and returned to bodies, and then shows him the line of Romans waiting to be born, down to Augustus. Aeneas leaves through the gate of false dreams, a detail that has provoked argument for two thousand years.
The poem's governing virtue is pietas, a word covering obligation to gods, father, son and destiny at once. Aeneas is defined by it and diminished by it: he abandons Dido because he is instructed to, and the poem gives her the better speeches. That tension is why readers still argue about whether the Aeneid endorses the empire it celebrates.
The ending sharpens it. Aeneas has Turnus at his mercy and is moved to spare him, then sees on his shoulder the belt stripped from a boy he had killed, and kills him in anger. The poem stops there, with no settlement, no marriage and no founding, on a line describing the resentful flight of a soul to the shades. Whether Virgil intended to write further is not knowable, but the twelve-book architecture is complete, and the abruptness reads as deliberate.