Alphabet Letters
Rho ρ
ROH
Also Known As Rho
Greek Letters
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Origin Adapted from Phoenician consonantal script, about the 8th century BCE
Rho is the seventeenth letter of the Greek alphabet, from the Phoenician resh, meaning head, and the ancestor of Latin R. It sounds the r, often rolled or with a breathy rh at the start of a word, and its value in isopsephy is one hundred, placing it one hundredth in the numeral order. The sequence jumps from Pi at eighty to Rho at one hundred because the number ninety belonged to the archaic letter koppa, the ancestor of Latin Q, which was kept only as a numeral and is not among the twenty-four classical letters. Combined with Chi, Rho forms the Chi-Rho, one of the earliest and most important Christian symbols, the first two letters of Christos, said to have appeared to the emperor Constantine before battle. In physics the lowercase rho denotes density, resistivity, and charge density; in mathematics it denotes a correlation coefficient and a radial coordinate.
Facts
Origins
Origin PeriodAdapted from Phoenician consonantal script, about the 8th century BCE 1Tradition: The Greek alphabet and the Milesian numerals Origin PeriodEvery European alphabet descends from that decision 1Tradition: The Greek alphabet and the Milesian numerals Origin PeriodInnovation: wrote vowels with letters of their own 1Tradition: The Greek alphabet and the Milesian numerals Place of OriginPrecise place disputed: Al Mina, Cyprus, Crete, Euboea all argued for 1Tradition: The Greek alphabet and the Milesian numerals Place of OriginThe Aegean world, at a point of contact with Phoenician traders 1Tradition: The Greek alphabet and the Milesian numerals Origin of the NameAlpha, beta, gamma are aleph, bet, gimel: ox, house, camel 1Tradition: The Greek alphabet and the Milesian numerals Origin of the NameClearest evidence the alphabet was taken over, not invented 1Tradition: The Greek alphabet and the Milesian numerals Origin of the NameGreek letter names are borrowed Semitic words meaning nothing in Greek 1Tradition: The Greek alphabet and the Milesian numerals Sense of the Namehead (from Phoenician resh) 1Tradition: The Greek alphabet and the Milesian numerals The pictographic sense is a modern reconstruction from the letter name rather than a meaning attested in the script's own period, and the atlas records that position elsewhere on this letter. The name itself is inherited; the picture behind it is inferred. Identity
Script TypeAn alphabet: each letter writes a single sound, consonant or vowel, inherited from Phoenician's twenty-two consonantal signs but repurposing several of them, for the first time in the alphabet's history, to write vowels outright. 1 PositionSeventeenth of twenty-four in the Greek alphabet 1 Attributions
Associated SoundLiquid r, often rolled, or a breathy rh at the start of a word 1 Attestation
Meaning in the Attesting SourceIsopsephy (Greek gematria) attested in inscriptions and magical papyri 1Tradition: The Greek alphabet and the Milesian numerals Meaning in the Attesting SourceThe 27-sign series used three lost letters: digamma/stigma, koppa, sampi 1Tradition: The Greek alphabet and the Milesian numerals Meaning in the Attesting SourceThis atlas's 24 letters hold none of those three 1Tradition: The Greek alphabet and the Milesian numerals Learn More
Rho: The Greek Letter (Value 100), from Head
Rho is the seventeenth Greek letter, from Phoenician resh ('head'); its value is 100. Rho carries genuine Christian symbolism as half of the Chi-Rho monogram, the superimposed first two letters of Christos (Christ) that the emperor Constantine placed on the labarum standard in the fourth century. The Greek letters doubled as numerals in the Milesian (alphabetic) system, in which each letter carried a fixed value; the practice of summing a word's letters into a number, called isopsephy, is the Greek counterpart of Hebrew gematria and appears in inscriptions, the Greek Magical Papyri and early Christian texts. Rho's Phoenician ancestry places it in a borrowing whose exact point of contact, somewhere among Al Mina, Cyprus, Crete and Euboea in the Aegean world, is still disputed, though the borrowing itself, conventionally dated to around the 8th century BCE, is agreed to be the ancestor of every European alphabet still in use, including the Latin one covered elsewhere in this atlas.
The Greeks' own contribution was to give vowels dedicated letters of their own, something the consonant-only Phoenician script never did. Its isopsephy value of 100 belongs to the Milesian alphabetic numeral system, which also needed three further, otherwise obsolete letters, digamma (also called stigma), koppa and sampi, to cover every value from 1 up to 900; none of the three survives among the 24 letters in ordinary use today.
Rho and the Chi-Rho Monogram
Rho's best-known symbolic use has nothing to do with its ordinary sound, covered elsewhere in this atlas, and everything to do with its shape: overlaid on chi, the first two letters of the Greek Christos, Christ, rho's single descending stroke and chi's crossed strokes combine into the Chi-Rho monogram, one of the oldest and most widespread symbols of Christianity.
Early Christian writers Eusebius and Lactantius, writing in the 4th century, both record that the emperor Constantine adopted the sign after a vision before the Battle of the Milvian Bridge in 312 CE, and the monogram subsequently spread across Christian art, coinage, and manuscripts throughout the late Roman and Byzantine world.
In modern technical use, physicists and engineers reserve lowercase rho for density and for electrical resistivity, and mathematicians occasionally use it for correlation coefficients in statistics, none of which draws on either the Chi-Rho tradition or on rho's ancient Semitic root resh, meaning head. Astronomers, following the Bayer star-naming convention of 1603, also use Rho to mark a constellation's seventeenth- or eighteenth-brightest star, continuing the same ranked sequence used throughout the Greek alphabet.
Cross-Tradition Connections
Derived from This
The Latin letter R descends from Greek Rho, reaching Latin through the Etruscan adaptation of a Western Greek alphabet. A straightforward continuation of shape, order and sound value.
Why this is disputed. Glagolitic Ritsi is read as Greek Rho's counterpart in an alphabet Cyril modeled on Greek order and numeral values, but which theory explains where its rounded letterform actually came from is a live paleographic dispute. The mainstream palaeographic school, developed since Isaac Taylor's nineteenth century study, derives Glagolitic's ornamental shapes from medieval Greek cursive minuscule redesigned for Slavonic use. A rival idiographic school reads Glagolitic as substantially an original invention, its shapes built from basic forms such as the cross, circle and triangle rather than borrowed from any existing script, so this specific correspondence to Rho is accepted by one camp and denied by the other.
Taken over into heavy native use; with lambda it separates r from l
Rtsy takes its shape from Greek rho and its numeral value of 100 from the same letter. From this point upward the Cyrillic and Glagolitic number series agree.
Related To
Roman R and Greek Rho continue the same Phoenician resh; Latin added a leg to the rounded Greek shape to keep it distinct from P.
Greek Rho and Hebrew Resh are cognates. Both continue the same Phoenician sign, which is why both carry the numeral value 200 in their letter-number systems. A shared ancestor, not a borrowing in either direction. The Greek alphabet was adapted from the Phoenician abjad in the early first millennium BC, and the Hebrew square script descends from the same abjad through Aramaic.
Hebrew Resh and Greek Rho continue the same Phoenician resh; both carry the numeral value 200 in their letter-number systems.
Samaritan Rish and Greek Rho both continue the same Phoenician sign, and both write r.
Coptic Ro is the Greek rho, writing the r sound that earlier Egyptian scripts could not distinguish from l; both carry the numeral value 100.
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