Encyclopedia Britannica – Roman Republic
https://www.britannica.com/place/Roman-Republic
A very concise overview of the history of the Roman Republic can be found on this page.
Plutarch: The Parallel Lives – The Life of Coriolanus
https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Plutarch/Lives/Coriolanus*.html
A full copy of Plutarch's Parallel Lives, on which Shakespeare's Coriolanus was based, can be found at this link.
University of Oxford Podcasts – Coriolanus
https://podcasts.ox.ac.uk/coriolanus
This audio lecture provides insight into the translation of the Coriolanus character from ancient sources to Shakespeare's play.