ERGASTULUM was a private prison attached to most Roman farms, called carcer rusticus by Juvenal (xiv.24), where the slaves were made to work in chains. It appears to have been usually under ground, and according to Columella (i.6) ought to be lighted by narrow windows, which should be too high from the ground to be touched by the hand. The slaves confined in an ergastulum were also employed to cultivate the fields in chains (Plin. H.N. xviii.7 §4; Flor. iii.19). Slaves who had displeased their masters were punished by imprisonment in the ergastulum; and in the same place all slaves who could not be depended on or were barbarous in their habits, were regularly kept. A trustworthy slave had the care of the ergastulum, and was therefore called ergastularius (Colum. i.8). According to Plutarch (Tib. Gracch. 8), these prisons arose in consequence of the conquest of Italy by the Romans, and the great number of barbarous slaves who were employed to cultivate the conquered lands. In the time of Hadrian and Antoninus, many enactments were made to ameliorate the condition of slaves; and among other salutary measures, Hadrian abolished the ergastula, which must have been liable to great abuse in the hands of tyrannical masters (Spart. Hadrian, 18, compared with Gaius, i.53). For further information on the subject, see Brissonius, Antiq. Select. ii.9; Lipsius, Elect. ii.15, Opera, vol. i p317, &c.; Gottling, Gesch. der Röm. Staatsv. p135.


William Smith, A Dictionary of Greek and Roman Antiquities (London: John Murray, 1875), 476.