A cognomen is a type of surname used in ancient Roman naming conventions. It typically followed the praenomen (given name) and the nomen (family name), serving to distinguish individuals within a family. For example, in the name Gaius Julius Caesar, "Caesar" is the cognomen. Cognomina often reflected personal characteristics, achievements, or even physical traits. Over time, they became hereditary, passed down through generations. This practice laid the groundwork for modern surnames, influencing how names are structured in many cultures today.