Agrippina the Younger (15-59 AD)

She survived the reign of Caligula, outlasted the emperor Claudius, and placed her own son on the throne of Rome. For a brief, remarkable period, Julia Agrippina was the most powerful woman the empire had ever seen - her face on the coins, her word effectively law.

What makes her story so difficult to settle is that almost everything written about her was written by people with reasons to destroy her reputation. Tacitus drew heavily on the memoirs of Agrippina's successor as empress - hardly a neutral source. Suetonius wrote decades after her death in a climate hostile to everything she represented.

Strip away the hostile testimony and what remains is a woman of extraordinary political intelligence who operated without any of the formal mechanisms men used to exercise power - and who came closer to holding it outright than any woman Rome had produced.

Nero had her killed in 59 AD. It took him three attempts.