Information for episode scripts came primarily from four sources:
Caesar: Life of a Colossus by Adrian Goldsworthy
Antony and Cleopatra by Adrian Goldsworthy
Augustus: First Emperor of Rome by Adrian Goldsworthy (this book was a big inspiration to start the series)
Ancient Rome: A New History by David Potter (my college textbook)
The basis of Death of the Roman Republic is built off of these books, but I also did some additional Internet research for every episode from reliable sources, to corroborate facts and expound on the story.