Wikipedia
Mettius is a Latin praenomen, or personal name, which was used in pre-Roman times and perhaps during the early centuries of the Roman Republic, but which was obsolete by the 1st century BC. The feminine form is Mettia. The patronymic gens Mettia was derived from this praenomen. The name was rare in historical times, and not regularly abbreviated.
The praenomen Mettius is known primarily from two individuals who lived during the earliest period of Roman history. Mettius Curtius was a Sabine warrior who fought under Titus Tatius during the time of Romulus, the founder and first king of Rome. During a major battle, the Sabine champion narrowly escaped drowning in a swampy area. Mettius Fufetius was the commander of the Alban forces during the war between Rome and Alba Longa, during the reign of Tullus Hostilius, the third king of Rome. His stalwart defense of the city against certain annihilation led to his brutal execution at the orders of Hostilius after the city was taken.
As with other rare praenomina, Mettius may once have been more widespread amongst the plebeians, and in the countryside. Other than the Curtii and Fufetii, the name is known to have been used by the obscure gens Scuilia, and must once have been used by the ancestors of gens Mettia.