Peter, Richard (1897–1902). "Orcus". In Roscher, Wilhelm Heinrich (ed.). Ausführliches Lexikon der griechischen und römischen Mythologie (in German). Vol.3.1. Leipzig, DE: Teubner. pp.coll. 940–945.
Servius, Commentarius in Donatum, p. 444, 21, and Probus, Catholica, p. 10, 22 ("exceptis tribus, quae Latina sunt, lurcho pulcher Orchus: sic enim in antiquioribus reperies, non Orcus"), both in Keil, Heinrich, ed. (1864). Grammatici Latini (in Latin). Vol.IV. Leipzig, DE: Teubner.; CIL II 488.
Hesiod, Theogony226–232; Works and Days 802–804: "ἐν πέμπτῃ γάρ φασιν Ἐρινύας ἀμφιπολεύειν / Ὅρκον γεινόμενον, τὸν Ἔρις τέκε πῆμ' ἐπιόρκοις" ("on the fifth, they say, the Erinyes attended the birth of Horkos, whom Eris bore as a bane to those who swear false oaths").