The Latin Q's descent from Phoenician qoph, by way of a Greek letter called qoppa, is covered elsewhere in this atlas. Qoppa represented a sound classical Greek came to treat as redundant with kappa, and it dropped out of ordinary Greek writing, surviving only as the numeral symbol for ninety, a fate discussed alongside Greek isopsephy elsewhere. Latin kept the letter, however, because its makers needed it for a genuine Latin sound distinct from that of C or K, and Rome narrowed its use to a single context: Q appears in classical and modern Latin-derived spelling only followed by U, as in qu-, a restriction with no parallel among the other consonants carried over from Phoenician.
The Roman capital Q, a circle with a short descending tail, is essentially qoph's own ancient shape with that tail added, and the lowercase q, formed in medieval cursive by extending the tail into a full descender below the line, mirrors the lowercase p's ascender-free, descender-bearing structure on the opposite side of the alphabet. Q carries no Roman numeral value and, unlike I, V, X, L, C, D and M, was never pressed into any parallel notational system in classical Rome, remaining throughout its history a plain consonant letter with no numeral or gematria-style overlay.