He was a senator, and very critical of Tiberius, regarding him as an unworthy successor to Augustus. His hyperbolic description of the treason trials could be linked to his anger at Domitian who he lived under and also conducted treason trials. He praised republican (democratic) systems such as more power being given to the senate.
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PROS:
* Great detail
* Access to actual documents and first hand accounts
* Analyses sources
CONS:
* Bias and hostility e.g. overcritical of Tiberius
* His focus is on senators and the upper classes, not the plebs