Antonia Caenis or Cenide, (died 74 AD) a former slave and secretary of Antonia Minor (mother of the emperor Claudius), was Roman emperor Vespasian's contubernalis.[1][2][3][4]

It could be thought that she had family in Istria, now in Croatia, based on a trip she took there (Suet. Dom. 12.3). In her 30s Caenis, still possibly a slave, was in an unofficial type of relationship with Vespasian, known as contubernium,[5] before his marriage. According to Suetonius, after the death of Vespasian's wife Flavia Domitilla, Vespasian and Caenis, now a freedwoman, resumed their relationship; she was his wife "in all but name" until her death in AD 74.

She had a remarkable memory and considerable influence on the emperor's administration, carried out official business on his behalf, and apparently made a lot of money from her position.[6] However, she was treated with disrespect by Vespasian's son Domitian, who refused to greet her as one of the family.[7]

The life of Caenis and her love-story with Vespasian is portrayed in Lindsey Davis' novel The Course of Honour. She is also a character who features regularly in Robert Fabbri's Vespasian series, where she is depicted as being the long lost grand-niece of the king of the Caenii, a rebelling tribe in Thracia.