I

I 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 vowel /i/ and the glide /j/. Historically it is from Phoenician yod ('hand') by way of Greek iota. 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 I the digit 9; 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 I's sound history, from Phoenician yod through Greek iota, is covered elsewhere; this entry follows two later, separate developments. Graphically, I served for both the vowel /i/ and the consonant /j/ throughout antiquity and the Middle Ages, since no separate letter for the consonant existed; the Italian grammarian Gian Giorgio Trissino is usually credited with proposing a graphic split into I and J in 1524, though the distinction spread through European printing only gradually over the following two centuries, and Theban and several other Renaissance-era ciphers covered elsewhere in this atlas still use one sign for both.

Separately, I is one of seven Latin letters reused as a Roman numeral, standing for one; the standard account holds that I, along with V and X, began as tally notches rather than as the alphabet's own letters, with a single I marking a unit and repeated strokes building up small numbers, a system distinct from and older than the alphabetic gematria and isopsephy traditions covered for Hebrew and Greek letters elsewhere in this atlas. Roman numeral I is not related to the letter's phonetic value and carries no comparable esoteric tradition of its own, unlike the tenth Hebrew letter yod, covered elsewhere in this atlas, whose numeral value of ten sits inside a much older gematria system.