Plutarch, Cicero
Bernadotte Perrin, Ed.

18. Accordingly, it was no trifling or insignificant plan which Lentulus was cherishing, nay, it was decided to kill all the senators and as many of the other citizens as they could, to burn down the city itself, and to spare no one except the children of Pompey; these they were to seize and hold in their own custody and keep as hostages for their reconciliation with Pompey; for already there was current a wide-spread and sure report of his coming back from his great expedition. [2] A night had also been fixed for the attempt, a night of the Saturnalia,¹ and swords, tow, and brimstone had been carried to the house of Cethegus and hidden there. Moreover, they had appointed a hundred men and assigned by lot as many quarters of Rome to each one severally, in order that within a short time many might play the incendiary and the city be everywhere in a blaze. Others, too, were to stop up the aqueducts and kill those who tried to bring water.

[3] But while this was going on, there chanced to be staying at Rome two ambassadors of the Allobroges, a nation which at that time was in a particularly evil plight and felt oppressed by the Roman sway. These men Lentulus and his partisans thought would be useful in stirring up Gaul to revolt, and therefore took them into the conspiracy. They also gave them letters to their senate, and letters to Catiline, making the senate promises of freedom and urging Catiline to set the slaves free and march upon Rome. [4] They also sent with them to Catiline a certain Titus of Croton, who was to carry the letters. But the conspirators were unbalanced men who seldom met together without wine and women, while Cicero was following their schemes industriously, with sober judgement and surpassing sagacity; he also had many men outside of their conspiracy who kept watch upon their doings and helped him track them down, and he conferred secretly and confidentially with many who were supposed to belong to the conspiracy; he therefore came to know of their conference with the strangers, [5] and, laying an ambush by night, he seized the man of Croton and his letters with the secret co-operation of the Allobroges.²