Family. The Latin word familia did not always correspond to our word family . Familia derives from famulia , and used to include in its meaning all the servants of a house, where there were at least fifteen. Familia also designated a body of workers organized and commanded by the prefect of waters. There were two of these bodies: one public, which Agrippa had instituted, and the other private, which was formed under Claudius. A band of gladiators who trained under a common leader was called a familia as well; the leader bore the name lanista .

Roman families ( familiae ) were segments of that which was called a gens . Thus Caecilius was the forebear who gave his name to the gens Caecilia , which comprised the families of the Balearici , Calvi , Caprarii , Celeres , Cretici , Dalmatici , Dentrices , Macedonici , Metelli , Nepotes , Numidici , Pii , Scipiones , Flacci , and Vittatores . There were both patrician and plebeian families, just as there were gentes patriciae and plebeiae . There were even those divided into a patrician branch and a plebeian branch ( partim nobiles , partim novae ), depending on whether they had possessed the ius imaginum since time immemorial or had only recently acquired it. It was possible to be born into a patrician family and fall into a plebeian one through degeneration, or to rise from a plebeian family into a patrician one, almost always by adoption. For this reason confusion reigns in Roman genealogies, made even greater by the identical names borne by both patrician and plebeian families . For instance, when the patrician Quintus Caepio adopted the plebeian Marcus Brutus, this Marcus Brutus and his descendants became patricians and the rest of the family of the Bruti remained plebeian. On the other hand, when the plebeian Quintus Metellus adopted the patrician Publius Scipio, the latter and all his descendants became plebeians, while the rest of the family of the Scipiones remained patrician. Freed slaves took on the family names of their masters and remained plebeians, another source of uncertainties. We must add to this that authors often used the words gens and familia interchangeably, some designating as a gens what others designate a familia , and vice-versa, but that which we have just outlined will suffice to warn against the errors into which it may be easy to fall.