@Plato in Phaedo introduces the idea that the proper practice of philosophy is "about nothing else but dying and being dead"
@Seneca's letters are full of reminders to meditate on death.
@Epictetus told his students that when kissing their child, brother, or friend, they should remind themselves that they are mortal, curbing their pleasure, as do "those who stand behind men in their triumphs and remind them that they are mortal"
@Marcus Aurelius in Meditations: "consider how ephemeral and mean all mortal things are"