I am currently confused about the definition of a primary and secondary source. Tacitus' Annals struck me as an example, I thought he was considered a primary source on the Roman empire. He describes Agrippina's 'supposed' murder of Claudius, however Tacitus was not present at the event. Is this actually a primary account?
Tactitus would not be considered a primary source. He was writing 100 years after the first events he describes in Annals. While that makes him a significantly more valuable source than a historian writing 400 years later, it's still something classicists must keep in mind and factor into anything he reports.