Neptūnus — the one true spelling, and the forms that fail it
A letter to a colleague, 31 July 2026 — on the name Neptūnus, and on the forms that keep failing it.
Your note said, roughly: surely the marks are a nicety. Permit me to use Neptūnus to show they are not.
First, the attestation. The attested form is NEPTVNVS, from the tradition's own record. The canonical transliteration is Neptūnus.
And the marks themselves: u → ū (Macron marks the long vowel). Remove any one of them and you have not simplified the name — you have told a small lie about it, and small lies in references have long consequences.
Say it aloud as the sources heard it: nep-TOO-nus, long ū on the stressed second syllable. The marks are what carry that sound to a reader who has never heard it spoken.
On the plain form — and I want to be precise, because you pushed on this. The plain form neptunus is not false — it is a fallback, and the register is exact about what that means. In systems that cannot carry diacritics (legacy databases, older tooling, parts of the address-bar pipeline) the flattened form is the accepted vehicle, and the rulebook names it explicitly as the final rung of the fallback hierarchy: full restoration first, circumflex where attested, macron-only by the academic standard, an attested variant, and only then plain ASCII.
What the fallback status forbids is promotion: neptunus may carry the name where marks are impossible, but it may not represent the name where marks are possible. Every mark it drops — u → ū — is a fact the sources recorded. A fallback is a vehicle, never the primary.
Now to the forms that provoked your letter. As for Neptunus: it comes from the publisher compromise — older books and hurried websites that print the "English equivalent" as if it were the name itself, and it fails because every substitution here (ū→u) is a romanization of convenience, not an attested spelling — it teaches the reader to guess, not to read As for Neptúnus: it comes from the near-miss — a form that looks right at a glance and circulates on wikis and forums, and it fails because a macron marks length; an acute marks tone — different facts
One more thing, because it always surprises: the name did not stay home. His equation with Poseidṓn is one of the oldest certain interpretatio Romana; his Etruscan substrate Nethuns appears on the Piacenza liver, the bronze model used to read omens. In the provinces he fused with local water powers — the Celtic river gods of Gaul and the Germanic North Sea powers — and his name became the standard gloss for "whatever god rules deep water here.
And it never stopped working. The planet Neptune — discovered by mathematics before telescopes (Adams and Le Verrier, 1846) — carries his name and trident symbol into every classroom. "Neptune's realm" is still navy slang for the open sea; the Order of Neptune initiates sailors crossing the equator; and the trident survives from Ukrainian heraldry to Maserati's badge.
The Convention's Own History
Every tradition in this register has its own scholarly transliteration standard, built by its own specialists over decades or centuries, and the register follows each on its own terms: Latin editorial convention, with Greek originals kept distinct from Roman reception. The principle that unifies them is the one the whole project stands on: a name is evidence, and evidence is not negotiable — not for keyboards, not for convenience, not for anyone.
Where Protocol Meets Practice
The technical answer is simple: the canonical marks are legal IDNA 2008 characters, encoded as punycode under `xn--`. The practical answer is messier: legal does not mean stocked (registrar inventory is partial), and stocked does not mean typeable (stacked diacritics defeat mobile keyboards).
So the register's rule is a hierarchy of attested forms — full restoration, circumflex, macron-only, attested variant, and finally plain ASCII for the systems that cannot carry marks. Every rung is defensible because every rung is attested. The forms this register rules against are not rungs; they are errors, and errors do not get rungs.
Write back when you have checked the sources; they are better company than I am.
— The Register
The Verdict
Neptūnus is the canonical form: attested, checkable, and enforced across the temple, the lexicon, the cards, the APIs, and this register. The plain form neptunus is sanctioned as the fallback vehicle and nothing more. The false forms above are documented so that no reader has to take the temple's word on faith — the violations are stated, the sources are named, and the register stands open to challenge on every line.
The temple of Neptūnus stands at /sites/neptunus/.
The docket for this ruling: 2 false forms ruled against, Neptunus first on the docket; 1 preserved mark verified: u → ū; no contested forms attested; the attestation rests on 6 cited sources — Lewis & Short, Varro, Horace.
The Register Continues
Entry 170 of 287 in the Canonical Register. Around it: the temple's founding dispatch, the Restoration File on the marks themselves, the Resonance File on the archetype at work, and the Rulebook behind all of it.
Continue the register — previous entry: Muspellheimr (read it) · next entry: Nézhā (read it).
The Canonical Register is written from the same canonical record as the lexicon itself. If a false form is missing from this page, it is because the evidence does not support calling it false — or because we have not seen it yet. Show us, with a citation, and the register will answer.