CARNIFEX, the public executioner at Rome, who put slaves and foreigners to death (Plaut. Bacch. iv.4.37; Capt. v.4.22), but no citizens, who were punished in a manner different from slaves. It was also his business to administer the torture. This office was considered so disgraceful, that he was not allowed to reside within the city (Cic. Pro Rabir. 5), but he lived without the Porta Metia or Esquilina (Plaut. Pseud. i.3.98), near the place destined for the punishment of slaves (Plaut. Cas. ii.6.2; Tac. Ann. xv.60; Hor. Epod. v.99), called Sestertium under the emperors (Plut. Galb. 20).
It is thought by some writers, from a passage in Plautus (Rud. iii.6.19), that the carnifex was anciently keeper of the prison under the triumviri capitales; but there does not appear sufficient authority for this opinion (Lipsius, Excurs. ad Tacit. Ann. ii.32).
Source: William Smith, D.C.L., LL.D., A Dictionary of Greek and Roman Antiquities, John Murray, London, 1875.