Buckler

Buckler front and back
Sword and buckler combat, plate from the Tacuinum Sanitatis illustrated in Lombardy, ca. 1390.
Irish round shield

A buckler (French bouclier 'shield', from Old French bocle, boucle 'boss') is a small shield, up to 45 cm (18 in) in diameter, gripped in the fist with a central handle behind the boss. It became more common as a companion weapon in hand-to-hand combat during the Medieval and Renaissance periods. Its size made it poor protection against missile weapons (e.g., arrows) but useful in deflecting the blow of an opponent's weapons, binding their arms, hindering their movements, or punching them.

Royal Armouries Ms. I.33 (c.1300 A.D.), considered the earliest extant armed-combat manual, describes a system of combat with buckler and sword.