Eclogue 4, also known as the Fourth Eclogue, is a Latin poem by the Roman poet Virgil. The poem is dated to 40 BC by its mention of the consulship of Virgil's patron Gaius Asinius Pollio.

The work predicts the birth of a boy, a supposed savior, who—once he is of age—will become divine and eventually rule over the world. The exact meaning of the poem is still debated. Earlier interpretations argued that the child was the hoped-for offspring of Mark Antony and Octavia the Younger. Some commentators shy away from imagining the child as a specific person. Edwin Floyd, for example, argued that the child could be seen metaphorically as Virgil's poetry. Another possibility, argued by Francis Cairns, is that the child is the expected offspring of Virgil's patron Gaius Asinius Pollio, to whom the poem is dedicated.

In late antiquity and the Middle Ages, the poem was reinterpreted by Christians to be about the birth of Jesus Christ. Medieval scholars thus claimed that Virgil had predicted Christ prior to his birth, and therefore must have been a pre-Christian prophet. Notable individuals such as Constantine the Great, St. Augustine, Dante Alighieri, and Alexander Pope believed in this interpretation of the eclogue. Modern scholars by and large shy away from this interpretation, although Floyd does note that the poem contains elements of religious and mythological themes, and R. G. M. Nisbet concluded that it is likely that Virgil was indirectly inspired by the Hebrew Scriptures via Eastern oracles.

The biographical tradition asserts that Virgil began the hexameter Eclogues (or Bucolics) in 42 BC and it is thought that the collection was published around 39–38 BC, although this is controversial. The Eclogues (from the Greek word for "selections") are a group of ten poems roughly modeled on the bucolic hexameters ("pastoral poetry") of the Hellenistic poet Theocritus. The fourth of these Eclogues can be dated to around 41 to 40 BC, during a time "when the clouds of civil war seemed to be lifting".

The 63-line poem (the shortest of the Eclogues) begins with an address to the Muses. The first few lines have been referred to as the "apology" of the poem; the work, much like Eclogue 6, is not so much concerned with pastoral themes, as it is with cosmological concepts, and lines 1–3 defend this change of pace. In line 4, the speaker refers to the Cumaean Sibyl as the source for his unfolding prophecy concerning the magnus ordo saeclorum, or "great order of the ages". The following lines (ll. 5–10) introduce a cluster of ideas: Hesiod's Ages of Man; the concept of a magnus annus, or the "Great Year" that begins a great "golden" age; the Italian idea of saecula; Plato's idea that there is a periodic rule of Saturn; and finally "eastern messianic" views similar to those found in the Sibylline Oracles, a collection of supposed oracular utterances written in Greek hexameters ascribed to the prophetesses who uttered divine revelations in a frenzied state.

"Now is come the last age of the Cumaean prophecy:
The great cycle of periods is born anew.
Now returns the Maid, returns the reign of Saturn:
Now from high heaven a new generation comes down.
Yet do thou at that boy's birth,
In whom the iron race shall begin to cease,
And the golden to arise over all the world,
Holy Lucina, be gracious; now thine own Apollo reigns."

Line 10 concludes with a reference to the god Apollo, a deity who would be elevated to a special place in the Roman pantheon during the rule of Augustus: tuus iam regnat Apollo ("Your Apollo now is ruling"). John Miller cautions, however, that this mention of Apollo—while the god's first "saecular [sic] appearance" in Latin literature—should not be read unequivocally as an allusion to Octavian, because c. 40 BC, both Octavian and Mark Antony were associated with the god, and that the former did not, at the time, enjoy "a monopoly on Apolline symbolism." R. G. M. Nisbet argued that the rule of Apollo (regnat Apollo) mentioned in line 10 should not be seen as contradicting the rule of Saturn (Saturnia regna) mentioned in line 6; they are merely expressing the same general idea using two different cosmological outlooks. The former is adhering to a newer, non-Hesiodic model, whereas the latter is referring to the older, Hesiodic version.

Both lines 11 and 13–14 mention Gaius Asinius Pollio's leadership, but line 11 refers to his consulship at the time of the poem's writing, whereas lines 13–14 seem to refer to a time when Pollio will "still be alive and prominent in the State when the child is well-grown" and when the Golden Age will have arrived. Lines 15–17 reveal that the child will become divine and eventually rule over the world. Lines 18–45 provide coverage of the boy's growth. At first, the child, in the cradle, will be allowed to enjoy munuscula, or little gifts. Importantly, the boy will grow skilled in reading, learning of the deeds of both heroes and his father. At this point in his life, the Golden Age will not have arrived in full; there will still be both sailing and walled towns, and thus, still war. Jenny Strauss Clay noted that the poem implies that the whole Heroic Age will have to be replayed; a new band of Argonauts will travel the seas, and a new Trojan War will occur. Given time, the need for sailing will dissipate. Then, the ground will grow more fertile: grapes will grow from brambles, oak trees will produce honey, corn will emerge from the ground by itself, poisonous plants and animals will disappear, and useful animals will be improved. Only when the need for agriculture ends will the Golden Age begin.