What is "mamertinus"

In ancient Rome, Mamertinus was a cognomen. Notable men named Mamertinus include:

• Marcus Petronius Sura Mamertinus, consul 182 AD
• Marcus Petronius Mamertinus, suffect consul 150 AD
• Claudius Mamertinus, consul 362 AD
• Mamertinus of Auxerre (d. ca. 462 AD), an abbot and saint

The carcer Mamertinus was a jail at the foot of the Capitol in Rome, supposed to have been built by Ancus Martius, fourth king of Rome, but not called by this name until the Middle Ages.