Vinculum (Latin meaning "link", "bond" or "tie") as a weapon refers to a length of heavy chain, often (but not always) fitted with weights at the end(s).
Ball & Chain (Pila et Vinculum)EditA long length of chain attached at one end to a fist-sized metal ball, typically studded with short spikes. This enables the chain to be used for entangling an opponent, while the weighted metal ball can be swung as a flail to shatter bones and crush skulls. Though a difficult weapon to control, a skilled user can twirl the ball and chain in the air like a lasso to keep attackers at bay, and the long chain gives them a far greater reach than a gladius or securis in the arena.
Chains have served as weapons in both the ancient and modern world. Whether purpose-designed (such as the Japanese Manriki-Gusari, Chinese chain whip or military flail) or a makeshift application of an everyday item (such as a simple "biker chain"), they function as both striking and entangling weapons.
Chains also feature as additional components in a variety of historical melee weapons (such as the Japanese Kusari-Gama), giving them multiple uses in combat.
In the episode Party Favors, Spartacus and Varro battle a large gladiator while chained to each other. Working together, the pair use their own chain as a weapon to entangle and kill their larger, heavily armored opponent.