
“We, on the contrary, make blessedness of life depend upon an untroubled mind, and exemption from all duties.”
Nos autem beatam vitam in animi securitate et in omnium vacatione munerum ponimus.
Shortened Version: We think a happy life consists in tranquility of mind.
Book I, section 6
De Natura Deorum – On the Nature of the Gods (45 BC)