Letters 41.3

If ever you have come upon a grove that is full of ancient trees which have grown to an unusual height, shutting out a view of the sky by a veil of pleached and intertwining branches, then the loftiness of the forest, the seclusion of the spot, and your marvel at the thick unbroken shade in the midst of the open spaces, will prove to you the presence of deity. Or if a cave, made by the deep crumbling of the rocks, holds up a mountain on its arch, a place not built with hands but hollowed out into such spaciousness by natural causes, your soul will be deeply moved by a certain intimation of the existence of God. We worship the sources of mighty rivers; we erect altars at places where great streams burst suddenly from hidden sources; we adore springs of hot water as divine, and consecrate certain pools because of their dark waters or their immeasurable depth.

Seneca, Letters to Lucilius 41.3, translated by Richard Mott Gummere