The partially preserved sixth book of the "Histories" by the Greek historian Polybius is considered one of the most important source texts, especially for ancient historians. It offers one of the most original ancient analyses of the constitution of the Roman Republic in the 2nd century BC. Notably significant is Polybius' methodology as he develops the theory of mixed constitution or applies models such as that of the cycle of constitutions. For study purposes, engaging with the original text, which is provided here, is essential.