There is more than one poem written of which every word begins with C. For example: (1) One composed by HUEBALD in honour of Charles le Chauve. It is in Latin hexameters and runs to somewhat more than a hundred lines, the last two of which are
Conveniet claras claustris componere cannas Completur clarus carmen cantabile CALVIS.
(2) One by HAMCONIUS, called “Certamen catholicum cum Calvinistis.” (3) One by HENRY HARDER, of 100 lines in Latin, on “Cats,” entitled: “Canum cum Catis certamen carmine compositum currente calamo C. Catulli Caninii.” The first line is-
“Cattorum canimus certamina clara canumque.”
Cats' canine caterwauling contests chant.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894