also called PORRIMA or PRORSA (Ov. Fast. 1.633; Gel. 16.16), together with Postvorta, are described either as the two sisters or companions of the Roman goddess Cannenta. (Ov. l.c.; Macr. 1.7.) It seems to be clear, from the manner in which Macrobius speaks of Antevorta and Postvorta, that originally they were only two attributes of the one goddess Carmenta, the former describing her knowledge of the future and the latter that of the past, analogous to the two-headed Janus. But that in later times Antevorta and Postvorta were regarded as two distinct beings, companions of Cannenta, or as two Carmentae, is expressly said by Varro (apud Gell. l.c.), Ovid, and Macrobius. According to Varro, who also says, that they had two altars at Rome, they were invoked by pregnant women, to avert the dangers of child-birth.
[L.S]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890