Plutarch, Cicero
Bernadotte Perrin, Ed.

15. Not long after this, when Catiline's soldiers in Etruria were already assembling and forming into companies, and when the day set for their attack was near, there came to the house of Cicero at midnight men who were the leading and most powerful Romans, Marcus Crassus, Marcus Marcellus, and Scipio Metellus; and knocking at the door and summoning the doorkeeper, they bade him wake Cicero and tell him they were there. [2] Their business was what I shall now relate. After Crassus had dined, his doorkeeper handed him some letters which an unknown man had brought; they were addressed to different persons, and one, which had no signature, was for Crassus himself. Crassus read this letter only, and since its contents told him that there was to be much bloodshed caused by Catiline, and advised him to escape secretly from the city, he did not open the rest, but came at once to Cicero, terrified by the danger, and seeking to free himself somewhat from charges that had been made against him on account of his friendship for Catiline.¹

[3] Cicero, accordingly, after deliberation, convened the senate at break of day, and carrying the letters thither gave them to the persons to whom they had been sent, with orders to read them aloud. All the letters alike were found to tell of a plot. And when also Quintus Arrius, a man of praetorian dignity, brought word of the soldiers who were being mustered into companies in Etruria, and Manlius was reported to be hovering about the cities there with a large force, in constant expectation of some news from Rome, [4] the senate passed a decree that matters should be put in the hands of the consuls, who were to accept the charge and manage as best they knew how for the preservation of the city.² Now, the senate is not wont to do this often, but only when it fears some great danger.