The Organization of the Roman Republic
The Romans never had a written constitution, but their form of their government, especially from the time of the passage of the lex Hortensia (287 B.C.), roughly parallels the modern American division of executive, legislative, and judical branches, although the senate doesn't neatly fit any of these categories. What follows is a fairly traditional, Mommsenian reconstruction, though at this level of detail most of the facts (if not the significance of, e.g., the patrician/plebian distinction) are not too controversial. One should be aware, however, of the difficulties surrounding the understanding of forms of government (as well as most other issues) during the first two centuries of the Republic.
Read More about The Organization of the Roman Republic