Complex sentence: The Second Catilinarian Conspiracy was a plot, devised by Catiline with the help of a group of aristocrats and disaffected veterans, to overthrow the Roman Republic in 63 BC. Cicero exposed the plot, which forced Catiline to flee from Rome.
Split into simpler sentences: The Second Catilinarian Conspiracy was a plot, devised by Catiline with the help of a group of aristocrats and disaffected veterans, to overthrow the Roman Republic. In 63 BC, Cicero exposed the plot which forced Catiline to flee from Rome.