Neither Neptune nor Poseidon were Indo-European

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You said:

Neptune was Roman, Poseidon was Greek. They came to be identified. Was that ancient (like Indo-European)?

ChatGPT said:

Yes—fairly ancient, but not as ancient as the shared Indo-European background itself.

Neptune and Poseidon were not originally the same god. Poseidon goes back very deep in Greek religion, already fully formed by the Mycenaean period (second millennium BCE). His name appears in Linear B tablets as Po-se-da-o-ne, and he was important enough that he may once have been a chief god, not just a sea god. Neptune, by contrast, seems to have been a much smaller, more local Italic deity, probably associated originally with fresh water—springs, rivers, irrigation—rather than the open sea.

The identification of Neptune with Poseidon happened later, through a process the Romans themselves called interpretatio graeca—the habit of mapping Roman gods onto Greek ones once Rome came under strong Greek cultural influence. This influence accelerated from about the 4th–3rd centuries BCE, as Rome expanded into southern Italy (Magna Graecia) and absorbed Greek literature, art, and theology. By the late Republic, educated Romans simply assumed Neptune was Poseidon under a Latin name.

So this is not a case where both gods descend cleanly from a single Indo-European sea god in the way, say, Dyeus underlies Zeus, Jupiter, and Dyaus Pitar. There may be very distant Indo-European water or storm motifs in the background, but Neptune’s early character doesn’t line up neatly with Poseidon’s. The convergence is largely cultural and intellectual, not genealogical.

In short: Poseidon is ancient in his maritime role; Neptune becomes maritime because of Poseidon. The identification is old by our standards—over two millennia—but it is a classical-period synthesis, not a Bronze Age inheritance.

You said:

Makes sense; the Mediterranean is Grecko-Roman, not Central Asian.

ChatGPT said:

Exactly. The religious “ecosystem” of the Mediterranean is coastal, urban, and trade-soaked, not steppe- or river-pastoral in the Central Asian sense. Gods there tend to accrete meaning around navigation, harbors, colonies, and imperial administration, and they cross-pollinate fast because sailors, merchants, and soldiers move constantly.

That’s why the Greco-Roman world ends up with a shared divine vocabulary even when the roots differ. Rome didn’t inherit a ready-made Indo-European sea god because early Latium wasn’t a seafaring culture in the way the Aegean was. Once Rome became Mediterranean—naval power, overseas provinces, grain fleets—it essentially imported Poseidon wholesale and “retrofitted” Neptune to match. Same with Aphrodite → Venus (with Near Eastern help), Ares → Mars (though Mars kept a very Roman moral spine), and Hermes → Mercury.

Central Asian or steppe traditions, by contrast, emphasize sky, oath, fire, horses, and wide land—very different pressures, very different mythic solutions. The Mediterranean gods are shaped less by ancestry than by salt water and commerce.

Put another way: Indo-European gives you the grammar; the Mediterranean writes the poetry.

You said:

In Caesar's day, were Neptune and Poseidon still differentiated? Did they have different stories?

ChatGPT said:

By Caesar’s day, educated Romans did not meaningfully differentiate Neptune from Poseidon at the level of theology or myth. For literary, philosophical, and explanatory purposes, Neptune was simply Poseidon under a Latin name. That identification was already well settled by the late Republic.

That said, there were differences—but they were differences of cult and emphasis, not of narrative identity.

In terms of stories, almost everything Romans told about Neptune was borrowed directly from Greek Poseidon myths: the contest with Athena for Athens, the trident, earthquakes, storms at sea, hostility to Odysseus, and so on. Roman poets did not preserve an independent Neptune myth-cycle the way they did, say, with early Mars or Janus. When Caesar or his contemporaries thought “Neptune,” the mental furniture was overwhelmingly Greek.

Where differentiation did persist was in religious practice and tone. Neptune had Roman festivals (notably the Neptunalia), Roman priestly oversight, and Roman companions such as Salacia (a personification of salt water) rather than Amphitrite. These figures, however, are thin abstractions rather than actors in stories. Neptune was also less emotionally vivid in Roman religion—more a power to be propitiated than a personality with a dramatic life.

This fits a broader Roman pattern. Rome was quite comfortable saying, in effect: “Our god is the same as yours, but we honor him in our way.” Interpretatio graeca collapsed mythic identity while allowing ritual distinctiveness to continue.

So the short answer is: by Caesar’s time, no—there were not two competing narrative beings. There was one sea god, Poseidon-Neptune, with Greek stories and Roman rites. Any remaining distinction lived in temples and calendars, not in myth.

You said:

From what you say there were no really Roman myths about him, just things from Greece.

ChatGPT said:

Yes—that’s essentially right, and it’s a good way to put it.

There were no substantial, home-grown Roman myths about Neptune in the way there were about Romulus, Numa, Janus, early Mars, or even Saturn. What Rome had, before Greek influence, was cult without narrative: a god to be honored at the right time, in the right way, for practical reasons (water, drought, heat), not a god whose life unfolded in stories.

Early Roman religion in general was like that. It was legalistic, procedural, and transactional—do ut des. Gods were powers (numina), not characters. Myth, in the Greek sense of elaborate divine biography, came later and largely came from Greece. When Romans wanted stories for Neptune, they simply used Poseidon’s, translated and lightly Romanized.

That’s why Neptune feels thin compared to Poseidon. Poseidon has temperament, grudges, family drama, narrative weight. Neptune mostly has functions: sea power, naval success, relief from summer heat. Even his festival, the Neptunalia, is about coping with drought, not celebrating a mythic deed.

So your summary is accurate: by the time we can really “see” Roman literature, Neptune is already wearing Greek clothes, and underneath them there isn’t much in the way of an indigenous Roman story-cycle. Rome borrowed the myths because it wanted them, not because it had lost its own.

It’s a revealing contrast: Greek religion tells stories to explain the world; Roman religion performs rituals to manage it. Neptune sits squarely on that fault line.

You said:

So they were later separate developments not derived, unlike others, from an Indo-European origin.

ChatGPT said:

Broadly speaking—yes, with one important nuance.

Poseidon and Neptune are best understood as later, separate developments, not as two clean descendants of a single, well-defined Indo-European sea god in the way Zeus/Jupiter clearly descend from Dyēus ph₂tḗr. Poseidon’s deep roots are Greek (already Mycenaean), while Neptune’s early roots are Italic and comparatively modest, and they only become “the same god” through historical contact, not inheritance.

The nuance is this: both cultures almost certainly inherited very general Indo-European ideas—water as a powerful, dangerous force; a divine association between water and fertility or destruction—but nothing like a specific, named sea deity that can be traced across branches. In other words, there may be a shared conceptual substrate, but not a shared god.

That contrasts sharply with the sky-father complex (Zeus/Jupiter/Dyaus), the dawn goddess (Eos/Aurora/Ushas), or even the storm-warrior figures, where linguistic, functional, and mythic continuities line up neatly. With Poseidon and Neptune, they don’t.

So your formulation is right and well-targeted: this is convergence, not divergence. Poseidon and Neptune grew separately, in different ecological and cultural settings, and only later were welded together by Greco-Roman synthesis. The sea itself—inescapable in the Mediterranean—did the rest.

You said:

The names are so different.

ChatGPT said:

Yes—and that’s actually one of the strongest clues that you’re right.

When two gods really are inherited from a common Indo-European source, the names usually betray it. Dyēus → Zeus / Jupiter, h₂éwsōs → Eos / Aurora, Perkʷūnos → Perun / Thor / Parjanya. You can see the phonetic bones lining up even after thousands of years.

With Poseidon and Neptune, there’s nothing like that.

Poseidōn is opaque even inside Greek. Ancient Greeks themselves argued about it. Modern scholars tentatively connect it to posis (“husband, lord”) and da (“earth”), giving something like “lord of the earth,” which fits his early chthonic and earthquake aspects—but even that is debated. What matters here is that it looks distinctively Greek and probably very old within Greek, not a transparent Indo-European inheritance.

Neptūnus, on the other hand, is clearly Italic/Latin and likely tied to an Indo-European root connected with wetness or moisture (nebh- or nep-), cousins to Latin nebula (“mist”) and perhaps Old Irish neph (“cloud”). That points to water in a broad, atmospheric or terrestrial sense—not a roaring Aegean god with a trident.

So the names don’t just differ; they point in different directions:

• Poseidon: an ancient Greek power, possibly once “earth-lord” and quake-maker.

• Neptune: a Latin god of wetness and water management, later promoted to sea god.

If they were siblings in the Indo-European family tree, the names would whisper it. Instead, they speak different languages entirely—and only later were forced into harmony by Roman classicism.

You said:

What do we see in other Indo-European cultures?

ChatGPT said:

What we see, once we look beyond Greece and Rome, is actually very revealing: there is no consistent Indo-European “sea god” at all.

Across Indo-European cultures, the divine emphasis clusters around sky, storm, fire, oath, fertility, and rivers, not the open sea. That pattern fits the likely ecology of early Indo-European speakers—pastoral, inland, river-oriented—rather than maritime. When later Indo-European peoples became coastal, they tended to improvise, borrow, or elevate local spirits instead of unpacking a ready-made ancestral deity.

You can see this almost everywhere. In Vedic India, the great water powers are rivers (like Sarasvati) and cosmic waters (Apas), while Varuna governs cosmic order and the waters abstractly, not as a seafaring god. In the Germanic world, there is no classical sea god at all—only figures like Njord, who is associated with the sea, wealth, and seafaring, but whose name and traits don’t line up with Greek or Roman gods and may reflect local or even non-Indo-European influence. Slavic traditions emphasize river and rain gods; the Baltic religions do something similar. Celtic cultures revere wells, springs, and rivers (often female), with the sea remaining religiously marginal despite Atlantic exposure.

The pattern is striking: water is sacred everywhere, but the sea is not central. When a maritime god does appear, he is usually late, region-specific, and narratively thin—or else shaped by borrowing. Poseidon is the outlier, and even he seems to have started as something broader and more chthonic before becoming the Aegean sea god par excellence.

So across Indo-European cultures we see continuity in how water is conceptualized—dangerous, fertile, binding—but not in a shared named sea deity. The Mediterranean forced the issue. The steppe never did.

That absence is as informative as any presence: it tells us what kind of world the Indo-European gods were first imagined to inhabit.

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