Fritz Fraf, Bacchic mysteries for the Oxford Classical Dictionary
During the Imperial epoch, several associations called themselves speîra. This term originated as the name of a tactical unit of the Ptolemaic army and later came to be the Greek term for the cohors of the Roman army; in a Dionysiac context, it occurs especially in Macedonia and the Black Sea region, but also in Rome. The occasional complex title of a “cohors of the Asians” (speîra Asianôn, 2nd century CE) or the “cohors of the Trajaniens” (Traianēsiôn, 2nd century CE) resonates with the way cohorts of the contemporary army were named and was chosen either because these associations brought together veterans or because the structure of the army offered itself as an easy template for such associations. The strict hierarchy of the larger associations of the Imperial age is visible in their quasi-military organization with archimústai and archibákchoi as their leaders (the same military template is manifest in the self-designation of some groups as speirai, spirae, the tactical unit of the Ptolemaic army). Boukólos can mark another, higher degree than the simple bákchos, exploiting the image of oversight and leadership implied in the term.