= Synagoge pi807, Photius pi1554 Theodoridis; cf. Hesychius pi4399-4400, Photius pi1551, and esp. the scholia to Euripides, Phoenician Women 1087 (web address 1), where the headword, masculine nominative plural of this participle, occurs.
This rare middle/passive present participle, from a verb purghre/omai, is related to the adjective purgh/rhs ('fitted with towers') and is glossed by LSJ (web address 2) as 'being shut up as in a tower'. The meaning, however, could be understood equally well in most cases as 'being shut up behind the towers [i.e. the city walls]', or -- as is appropriate to the present gloss -- 'staging a defense from the towers [sc. city walls]'. Most attestations occupy an ambiguous position between these connotations, including the Euripides passage cited above, as well as Euripides' probable model, Aeschylus, Seven against Thebes 22 (web address 3) and 184 (web address 4), and Euripides, Orestes 1574 (web address 5).