The siege artillery is intended to evacuate the fortresses and to operate on the rear of the enemy. (The general is mounted on a clystère or syringe suitable for enemas, which turns out to be a recurrent theme of contemporary French political satire.)
(La Caricature, Paris, 1831.) (See also this version from 1833.) (This British print from 1800-1805 is the earliest Anglophone satirical invocation I’ve found of the disgust which this mechanism could induce.)

The earliest French clystère cartoon I’ve found is entitled “Trendy physician, or the colic of those medical gentlemen who have seen their urine and said that they are very sick.” (via Gallica, 1784)