<p>This was the only public prison in Rome, used as a place of brief detention and execution, not for long imprisonment. Sources use two terms, <i>Carcer</i> and <i>Tullianum</i>, but these are not strictly synonymous. The former refers to the whole; the latter refers to a part located underground: <i>est in carcere locus, quod Tullianum appellatur . . . circiter duodecim pedes humi depressus</i>, ‘within the prison is a spot, which is called Tullianum ... located about 12 feet underground’ (Sall., <i>Cat</i>. 55.3; cf. Festus 490; Varro, <i>Ling.</i> 5.151). Its location is given as <i>imminens foro</i>, ‘touching the Forum’ (Livy 1.33.8), close to the Temple of *Concordia Augusta (Dio Cass. 58.11.4), and next to the steps that led up to the *Arx (Val. Max. 6.3.3; Dio Cass. 58.5.6). From the literary testimonia (for which see Coarelli 1985, 67-72), we may identify the Carcer with the building under the Church of S. Giuseppe dei Falegnami. It fits the known location of the Carcer and preserves the architectural division between an upper and a lower level. Underneath is a well-preserved circular chamber (diam. 7 m) for which Coarelli (1985, 66) records a date of <i>c</i>. 300 B.C. Around 100 B.C. a flat-arched roof was added and a trapezoidal chamber built above, its outer walls oriented along the axes of the Temple of Concordia Augusta to the S and the *Comitium to the E (Coarelli 1985, 66-67, 74). Both upper and lower levels stood beneath ground level, so the Carcer was defined more by its interior than exterior space (see Coarelli 1985, 64 fig. 10). It may also have been part of a larger complex (Le Gall). Our map follows the standard convention of representing the upper level and front façade in isolation; the circular lower chamber is not shown.</p>