Lewis & Short

Carmentis, is (Carmenta, ae, Liv. 1, 7, 8 Weissenb. ad loc.; Hyg. Fab. 277), f. [carmen, q. v.], a Roman goddess of prophecy, acc. to mythologists, the mother of Evander, who went with him from Arcadia to Latium (hence Arcadia dea, Ov. F. 1, 462: Parrhasia dea, id. ib. 1, 618: Tegeaea parens, id. ib. 1, 627: Tegeaea sacerdos, id. ib. 6, 531, and Maenalis nympha, id. ib. 1, 634), and uttered oracles on the Capitoline Hill, Ov. F. 1, 462 sq.; Liv. l. l.; 5, 47, 2; Hyg. Fab. 277; Verg. A. 8, 336 sq., and Serv. ad h. l.
Also represented as two goddesses, Carmentes, and under the especial names Postverta and Prorsa (the backwards and forwards looking goddess), Varr. ap. Gell. 16, 16; Serv. ad Verg. l. l.
Hence,

    1. 1. Car-mentālis, e, of or pertaining to Carmentis: flamen, Cic. Brut. 14, 56: porta, a gate at Rome, near the temple of Carmentis, in the eighth district, through which the Fabii marched to the contest so destructive to themselves, Liv. 2, 49, 8; 24, 47, 15; 25, 7, 6; Verg. A. 8, 338; hence, as ominous, also called Porta Scelerata, Fest. p. 334, a; 335 and 284, a Müll.; cf. Ov. F. 2, 201, and Nieb. Röm. Gesch. 2, p. 222.
    2. 2. Subst.
  1. A. Carmentālĭa, ĭum, n., the festival of Carmentis, celebrated on the 11th and 15th of January, Varr. L. L. 6, § 12; Kalend. ap. Inscr. Orell. 2, p. 382; cf. Macr. S. 1, 16.
  2. B. Carmentārĭi, the priests of Carmentis, Serv. ad Verg. A. 8, 336.