ribaudequin

from The Century Dictionary.

• noun Originally, a cart or barrow plated with iron or other material to protect it from fire, and armed with long iron-shod pikes; a movable cheval-de-frise.
• noun A similar cart armed with a large crossbow, or with a small cannon in the fifteenth century.
• noun Hence— The cannon itself so used.

from the GNU version of the Collaborative International Dictionary of English.

• noun An engine of war used in the Middle Ages, consisting of a protected elevated staging on wheels, and armed in front with pikes. It was (after the 14th century) furnished with small cannon.
• noun A huge bow fixed on the wall of a fortified town for casting javelins.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An engine of war used in the Middle Ages, consisting of a protected elevated staging on wheels, and armed in front with pikes. After the 14th century it was furnished with small cannon.
• noun A huge bow fixed on the wall of a fortified town for casting javelins.