TheClaudian letters were developed by theRoman emperorClaudius (reigned 41–54). He introduced three new letters to theLatin alphabet:

• Ↄ or/X (antisigma) to replace BS[bz] and PS[ps], much asX stood in for CS[ks] and GS[ɡz]. The shape of this letter is disputed, however, since no inscription bearing it has been found.Franz Bücheler identified it with the variantRoman numeral Ↄ,^[2] but 20th-century philologists, working from copies ofPriscian's books, believe it to instead resemble two linked Cs (Ↄ+Ϲ), which was a preexisting variant of Greeksigma, and easily mistaken for X by later writers.Revilo P. Oliver argued that Claudius would have based this letter upon the Arcadian variant ofpsi or.^[1] This letter should not be confused with the "open O" letter. (Ɔ)
• Ⅎ, a turned F ordigamma (digamma inversum) to be used instead of the letter V when denoting the consonantal phoneme[w] or[β].^[2] Thus, it resembles the use of the letterV in modern Latin texts, where the vocalic use of the letter V is represented by its variantU, which has been recognized as a different letter only later.
• Ⱶ, a half H. The value of this letter is unclear, but it may have represented the so-calledsonus medius, a short vowel sound (likely[ɨ] or[ʉ]) used beforelabial consonants in Latin words such asoptumus andoptimus. The letter was later used as a variant of[y] in inscriptions for short Greekupsilon (as inOlympicus). It may have disappeared because thesonus medius itself disappeared from spoken language.^{[1][citation needed]}

There are some examples found of Ⅎ and Ⱶ being used during Claudius' reign, but as said before, there are no examples of Ↄ being used since the letter had no unique purpose as its sound could be spelt either asPS orBS with no apparent issues.

• Examples of Ⅎ:AMPLIAℲIT,ARℲALES,ARℲALIVM,^[3]BOℲE,IOℲI,TERMINAℲITQVE,VOℲIMVS,ℲELINA,ℲIR, ℲOℲEMVS.^[4][5]
• Examples of Ⱶ:BⱵBLIOTHECA,CⱵCNVS,MAXⱵMVS,OPTⱵME, and once inGⱵBERNATOR.^[4][6]

These letters were used to a small extent on public inscriptions dating from Claudius' reign, but their use was abandoned after his death.^[7] Their forms were probably chosen to ease the transition, as they could be made from templates for existing letters. He may have been inspired by his ancestorAppius Claudius theCensor, who made earlier changes to the Latin alphabet.^[8] Claudius did indeed introduce his letters during his own term as censor (47–48), using arguments preserved in the historianTacitus' account of his reign, although the original proclamation is no longer extant.Suetonius said of Claudius' letters:

Besides this he [Claudius] invented three new letters and added them to the alphabet, maintaining that they were greatly needed; he published a book on their theory when he was still in private life, and when he became emperor had no difficulty in bringing about their general use. These characters may still be seen in numerous books, in the [state] registers, and in inscriptions on public buildings.^[9]

Support for the letters was added in version 5.0.0 ofUnicode.^[10] Although these letters, as all Latin letters in antiquity, originally occurred only in capital form, lowercase forms were introduced to meet Unicode casing requirements.^[10] The minuscule form for the turned F was designed as a turned small capital F and should not be confused with theIPA symbolɟ representing a voiced palatal stop.

The letters are encoded as follows:

• Chinese characters of Empress Wu
• Reversed half H – Letter of the Latin alphabet

• Palaeographic letters
• Latin-script letters
• Claudius
• 1st-century introductions
• Latin epigraphy

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