It refers to this story:
QuoteAs a young military tribune, he defeated a giant Gaul in single combat in one of the most famous duels of the Republic, which earned him the cognomen Torquatus after the torc he took from the Gaul's body....
In 361 BC, Titus Manlius fought in the army of Titus Quinctius Poenus Capitolinus Crispinus against the Gauls during the Battle of the Anio River. When a Gaul of enormous size and strength challenged the Romans to single combat, Manlius accepted the challenge with the approval of Poenus after the rest of the army had held back from responding for a long period of time. Despite being physically inferior, he killed the Gaul with blows to the belly and groin, after which he stripped the corpse of a torc and placed it around his own neck. From this, he gained the agnomen Torquatus, a title that was passed down also to his descendants.
A torc/torque is a heavy necklace worn by the Celtic tribes. Torque -- hence Torquatus.
QuoteBecause (Titus Manlius) always wore (the torque he took from the Gaul), he received the nickname Torquatus (the one who wears a torc),[23] and it was adopted by his family.
