Καῖσαρ, the name of a patrician family of the Julia gens, which was one of the most ancient in the Roman state, and traced its origin to Iulus, the son of Aeneas. [JULIAGENS.] It is uncertain which member of this gens first obtained the surname of Caesar, but the first who occurs in history is Sex. Julius Caesar, praetor in B. C. 208. The origin of the name is equally uncertain. Spartianus, in his life of Aelius Verus (100.2), mentions four different opinions respecting its origin : 1.That the word signified an elephant in the language of the Moors, and was given as a surname to one of the Julii because he had killed an elephant. 2. That it was given to one of the Julii because he had been cut (caesus) out of his mother's womb after her death; or 3. Because he had been born with a great quantity of hair (caesaries) on his head; or 4. Because he had azure-coloured (caesii) eyes of an almost supernatural kind. Of these opinions the third, which is also given by Festus (s. v. Caesar), seems to come nearest the truth. Caesar and caesaries are both probably connected with the Sanskrit kêsa, " hair," and it is quite in accordance with the Roman custom for a surname to be given to an individual from some peculiarity in his personal appearance. The second opinion, which seems to have been the most popular one with the ancient writers (Serv. ad Virg. Aen. 1.290; Plin. Nat. 7.7. s. 9; Solin. 1.62; Zonar. 10.11), arose without doubt from a false etymology. With respect to the first, which was the one adopted, says Spartianus (l.c.), by the most learned men, it is impossible to disprove it absolutely, as we know next to nothing of the ancient Moorish language : but it has no inherent probability in it; and the statement of Servius (l.c.) is undoubtedly false, that the grandfather of the dictator obtained the surname on account of killing an elephant with his own hand in Africa, as there were several of the Julii with this name before his time.

An inquiry into the etymology of this name is of some interest, as no other name has ever obtained such celebrity--"clarum et duraturum cum aeternitate mundi nomen." (Spart. Ael. Ver. 1.) It was assumed by Augustus as the adopted son of the dictator, and was by Augustus handed down to his adopted son Tiberius. It continued to be used by Caligula, Claudius, and Nero, as members either by adoption or female descent of Caesar's family; but though the family became extinct with Nero, succeeding emperors still retained it as part of their titles, and it was the practice to prefix it to their own name, as for instance, Imperator Caesar Domitianus Augustus. When Hadrian adopted Aelius Verus, he allowed the latter to take the title of Caesar; and from this time, though the title of continued to be confined to the reigning prince, that of Caesar was also granted to the second person in the state and the heir presumptive to the throne.

In the following stemma the connexion of the earlier members of the family is to a considerable extent conjectural. A full account of the lives of all the Caesars mentioned below is given in Drumann's Geschichte Roms, vol. iii. p. 113, &c.