Munatia Plancina (died 33 AD) was a Roman noblewoman who lived in the early times of the Empire founded by Augustus. She was the wife of the governor of Syria, Gnaeus Calpurnius Piso. The couple was accused of poisoning Germanicus, the nephew and adopted son of the Emperor Tiberius. At first, Munatia Plancina was acquitted, but when the trial was renewed she committed suicide.
Often Munatia Plancina is simply called Plancina. She was probably the daughter of a certain Munatius, who was the Comes of Tiberius at his diplomatic mission in the East. In this case she was the granddaughter of Lucius Munatius Plancus, who had been consul in 42 BC.
Munatia Plancina was a rich woman and very self-confident because of her noble descent. She was probably the second wife of Gnaeus Calpurnius Piso. They had two sons: Gnaeus, who later changed his first name into Lucius, and Marcus Calpurnius Piso. Munatia Plancina was also a close friend of Livia, the wife of the Emperor Augustus and mother of his successor Tiberius. When her husband was elected governor of Syria she accompanied him in his province (18 AD). At this time Germanicus traveled with an extraordinary command in the east of the Roman Empire, and he was accompanied by his wife Agrippina the Elder. They arrived at Syria and got involved in a serious quarrel with the governor Piso and his wife. Like Agrippina also Munatia Plancina was sometimes present at military parades. She often said insulting words against Germanicus and his wife. The Roman historian Tacitus states that Livia secretly ordered Munatia Plancina to take this action against Germanicus and Agrippina, but Tacitus’ account is not reliable. Munatia Plancina was supposed to have been in contact with a Syrian preparer of poison called Martina. When Germanicus soon died (10 October 19 AD) he allegedly suspected Piso and his wife of having him poisoned. The death of Germanicus supposedly gave Munatia Plancina a lot of pleasure. Then she supported her husband Piso to take again possession of Syria by military actions.
In autumn of 20 AD Munatia Plancina and her husband returned to Rome. The couple had to answer to the senate for their supposed murder of Germanicus. Allegedly Munatia Plancina was convicted of very serious crimes. But her powerful friend Livia fought for her and exerted pressure on Tiberius. Therefore, her acquittal was foreseeable and she dissociated herself from her husband Piso who committed suicide. A recently discovered senate resolution also confirms that Munatia Plancina owed her impunity to the recommendation of Tiberius, who had been pressed by Livia to act in this way. But after the death of Livia she had no longer such a powerful protectress. So in 33 AD Tiberius renewed the charge. She committed suicide before the judgement. 
The fact that the family of Munatia Plancina probably enjoyed only a low reputation during the reign of Tiberius can be concluded from the very negative characterization of her grandfather Lucius Munatius Plancus by the historian Marcus Velleius Paterculus.
- Der Neue Pauly, vol. 7, col. 468
- Tacitus, The Annals 2.43
- Tacitus, The Annals 3.16
- Tacitus, The Annals 2.55
- Tacitus, The Annals 2.43
- Tacitus, The Annals 2.82
- Tacitus, The Annals 2.74
- Tacitus, The Annals 2.71
- Cassius Dio, Roman History 57.18.9
- Tacitus, The Annals 2.75
- Tacitus, The Annals 3.13
- Tacitus, The Annals 2.80
- Tacitus, The Annals 3.9
- Tacitus, The Annals 3.15 compare 3.17
- Senatus Consultum de Cn. Pisone patre, lines 109-120
- Tacitus, The Annals 6.26
- Cassius Dio, Roman History 58.22
- Marcus Velleius Paterculus, Roman History 2.83
- Rudolf Hanslik: Munatius 44). In: Realencyclopädie der Classischen Altertumswissenschaft, vol. XVI 1 (1933), col. 556-557.
- Munatia Plancina. In: Der Neue Pauly (English: Brill’s New Pauly), vol. 7 (1999), col. 468.