The Byzantine Treatise De magistratibus populi Romani by Joannes Lydus provides wide and reliable informations about the ancient office of quaestores parricidii, as well as an interesting paretymology of the word parricida, whose origin is still unsolved. A philological consideration of the varia lectio contained in the codex unicus Caseolinus (Bibl. Nat. suppl. gr. 257; IX-X century), allows to argue for the existence of an early Latin form (quaestores) pārĭcīdiī with ancient /a:/ in the first syllable followed by a single /r/. Therefore, the standard Latin parricida with /rr/ must be considered a secondary form.