This article is concerned with a gigantic unpublished dictionary of Ancient Greek, most probably compiled at Alexandria during the first half of the sixth century ad. The dictionary is ascribed to Patriarch Cyril of Alexandria, an ascription strongly doubted. It is the first Greek dictionary which unites entries (usually rare ancient Greek words) found in Christian as well as pagan writers. The article investigates the ideology of the lexicon, which is strongly Christian, but also displays a warm acceptance of the classical literary past. The lexicon became the most influential in the history of Greek lexicography, having influenced almost all medieval Greek lexica (Hesychius, Synagoge, Photius, Suda, Zonaras and others). The article assembles all the information available today concerning the complicated history of scholarship on the lexicon, whose 200 preserved manuscripts and different surviving receptions have long puzzled scholars.