thumb|right|Use of san in archaic [[Ancient Corinth|Corinthian script: incised shard with a list of names, c.700 BC. The text reads:
<poem lang="grc-x-doric">
]........ΑΝ ΑΝΤΑΣ⁞ΧΑ.[
]....ΚΕΑΣ⁞ΑΝΓΑΡΙΟΣ[
]...ΑΥϜΙΟΣ⁞ΣΟΚΛΕΣ⁞[
].ΤΙΔΑΣ⁞ΑΜΥΝΤΑΣ[
]ΤΟΙ ΜΑΛΕϘΟ⁞ΚΑΙ.[
</poem>
Note the use of san at the end of most names, and the difference between san and mu (with a shorter right stem, x16px) in the word "ΑΜΥΝΤΑΣ".]]
thumb|right|Use of san in archaic [[Sicyonian writing: shard incised with the dedicatory inscription (Attic spelling , "of the hero"), using san together with eta (), and a characteristic Sikyonian X-shaped form of epsilon.]]
San () is an archaic letter of the Greek alphabet. Its shape can be described as a sigma () turned sideways. It was used as an alternative to sigma to denote the sound . Unlike sigma, whose position in the alphabet is between rho and tau, san appeared between pi and koppa in alphabetic order. In addition to denoting the archaic character, the name "san" also came to be used for sigma itself.
Historical use
Sigma and san
The existence of the two competing letters sigma and san is traditionally believed to have been due to confusion during the adoption of the Greek alphabet from the Phoenician script, because Phoenician had more sibilant sounds than Greek had. According to one theory, the distribution of the sibilant letters in Greek is due to pair-wise confusion between the sounds and alphabet positions of the four Phoenician sibilant signs: Greek sigma got its shape and alphabetic position from Phoenician shin (), but its name and sound value from Phoenician samekh. Conversely, Greek xi () got its shape and alphabetical position from samekh (), but its name and sound value from shin. The same kind of pair-wise exchange happened between Phoenician zayin and tsade: Greek zeta has the shape and position of zayin (𐤆) but the name and sound value of tsade, and conversely Greek san has the approximate shape and position of tsade (𐤑) but may originally have had the sound value of zayin, i.e. voiced . "san" was indeed the original name of what is now known as sigma, and as such presents a direct representation of the corresponding name "shin" in that position. This name was only later also associated with the alternative local letter now known as "san", whose original name remains unknown. The modern name "sigma", in turn, was a transparent Greek innovation that simply meant "hissing", based on a nominalization of a verb (, from an earlier stem , meaning 'to hiss').
Moreover, a modern re-interpretation of the sound values of the sibilants in Proto-Semitic, and thus in Phoenician, can account for the values of the Greek sibilants with less recourse to "confusion". Most significant is the reconstruction of shin as and thus also the source of the sound value of sigma; in turn, Samekh is reconstructed as the affricate , which is a better match for the plosive-fricative cluster value of xi.
{|class="wikitable"
|-
!colspan="6"|Phoenician
!colspan="5"|Greek
|-
!colspan=2|shape
!position
!name
!traditional <br> sound
!sound <br> after Kogan Athenaeus in his Deipnosophistae (c.200 AD) quotes an epigram which contained the spelled-out name of the philosopher Thrasymachus, still using san as the name for sigma:
<span class="anchor" id="Tsan"></span>Arcadian tsan
thumb|right|50px|Arcadian "ts"
A unique letter variant (shaped similarly to modern Cyrillic И, but with a slight leftward bend) has been found in a single inscription (therefore a hapax legomenon) in the Arcadocypriot dialect of Mantineia, Arcadia, a 5th-century BC inscription dedicated to Athena Alea (Inscriptiones Graecae V.ii.262) It is widely assumed to be a local innovation based on san, although Jeffery (1961) classes it as a variant of sigma. It appears to have denoted a sound and has been called tsan by some modern writers.
Modern use
thumb|right|The letter san as it appears in four basic fonts: [[Times Roman|Times New Roman, Lucida Grande, Arial, and Helvetica]]
In modern editions and transcriptions of ancient Greek writing, san has rarely been used as a separate letter. Since it never contrasts systematically with sigma except in abecedaria, it is usually silently regularized to sigma in modern editorial practice. In the electronic encoding standard Unicode, a pair of uppercase and lowercase forms of the letter was introduced in version 4.0 (2003). For this purpose, new lowercase forms for modern typography, for which no prior typographic tradition existed, had to be designed. Most fonts have adopted the convention of distinguishing uppercase san from mu by having its central V-like section descend only halfway down above the baseline, and lowercase san by giving it a left stem descending below the baseline. (Note that in historical epigraphic practice it was the other way round, with san being symmetrical and mu having a longer left stem.)
Unicode
San is encoded in Unicode, but the Arcadian "tsan" variant is unified with the identical-looking Pamphylian digamma since version 5.1.