X

X is a letter of the Latin (Roman) alphabet, the script now used to write English and most languages of western Europe and, today, much of the world. It represents the cluster /ks/. Historically it is from a Western Greek letter (related to chi and xi) by way of Etruscan. Unlike the Hebrew and Greek alphabets, the Latin (Roman) alphabet never developed a systematic per-letter mystical or numerological tradition: Roman numerals form a separate, non-alphabetic system, so this entry stays with the letter's linguistic and historical record. The Roman alphabet is the youngest of the three historical scripts covered in this atlas: Latium adapted it around the 7th century BCE from a west Greek alphabet, reaching it through Etruscan intermediaries who had themselves taken their letters from Greek colonists settled in the bay of Naples. Latin calls each letter simply by its sound rather than by an inherited name, unlike Hebrew and Greek, and it never built an alphabetic numeral system of its own, so there is no ancient Latin counterpart to Hebrew gematria or Greek isopsephy; Roman numerals are a separate, non-alphabetic notation.

A modern practice called name numerology, drawn from a twentieth-century repeating 1-to-9 chart and commonly marketed as Pythagorean despite no documented link to Pythagoras, assigns the letter X the digit 6; a rival popular scheme, the so-called Chaldean system, assigns different digits to the same letters, so even the two modern schemes disagree with each other.

The Latin X's descent from Greek chi is covered elsewhere in this atlas, but the relationship is more complicated than a simple borrowing. Classical Athenian Greek used chi for an aspirated /kh/ sound, but the western Greek alphabets of southern Italy, the ones Etruscan and Rome actually drew their letters from, used the same X-shaped letter for the very different consonant cluster /ks/, the value Latin inherited and English still uses. Because Etruscan and early Latin already had other letters covering the sounds Athenian chi represented, X entered the Roman alphabet carrying only its western Greek value, and Latin placed it near the end of its native letter sequence, roughly corresponding to the position once held by the Phoenician letter samekh, which classical Greek instead used for its own letter xi.

The Roman capital X, two crossed diagonal strokes, has remained essentially unchanged since antiquity, and it does double duty, like I, V, L, C, D and M, as a Roman numeral: X stands for ten, a value the standard account derives, like I and V, from an ancient tally notch rather than from the alphabetic letter's own history. That numeral use, quite apart from the letter's phonetic role, is also why a mark meant to stand in for an unknown or unwritten signature is conventionally an X, a habit going back at least to medieval documents signed by people who could not write their own name.