Ab urbe condita
Titus Livius (Livy)
Livy. History of Rome, Volumes 1-2. Roberts, Canon, Rev, translator. London, New York: J. M. Dent and Sons; E. P. Dutton and Co., 1912.
The Vestal was forcibly violated and gave birth to twins. She named Mars as their father, either because she really believed it, or because the fault might appear less heinous if a deity were the cause of it.