Illustrated Companion to the Latin Dictionary/Ergastularius

This article incorporates text from a publication now in the public domain: Rich, Anthony (1849). The illustrated companion to the Latin dictionary, and Greek lexicon. p. vi. OCLC 894670115. https://archive.org/details/illustratedcompa00rich. 

ERGASTULA'RIUS. A person who had the charge of superintending an ergastulum, and the slaves confined in it. He acted as a gaoler and taskmaster, to see that their work was done, and was himself a slave, though placed in a confidential office. Columell. i. 8. 17.