A nation can survive its fools, and even the ambitious. But it cannot survive treason from within. For the traitor appears not a traitor — he speaks in the accents familiar to his victims, and he appeals to the baseness that lies deep in the hearts of all men. He rots the soul of a nation — he works secretly and unknown in the night to undermine the pillars of the city — he infects the body politic so that it can no longer resist. A murderer is less to be feared. The traitor is the carrier of the plague. You have unbarred the gates of Rome to him.

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

(Spurious)

This text, widely passed around on social media, was made up for Cicero in Taylor Caldwell, A Pillar of Iron (1965).