Lucan's Marseilles grove

A grove there was, never profaned since time remote,
enclosing with its intertwining branches the dingy air
and chilly shadows, banishing sunlight far above.
In this grove there are no rustic Pans or Silvani,
masters of the forests, or Nymphs, but ceremonies of the gods
barbarous in ritual, altars furnished with hideous offerings,
and every tree is sanctified with human blood.
If antiquity at all deserves credence for its awe of the gods,
the birds fear to sit upon those branches,
the beasts fear to lie in those thickets; on those woods
no wind has borne down or thunderbolts shot from black
clouds; though the trees present their leaves to no breeze,
they have a trembling of their own. Water pours
from black springs and the grim and artless
images of gods stand as shapeless fallen tree-trunks.
The decay itself and pallor of the timber now rotting
is astonishing; not so do people fear deities worshipped
in ordinary forms: so much does ignorance of the gods
they dread increase their terror. Now it was rumoured that often the hollow caves below rumbled with earth-quakes,
that yew-trees fell and rose again,
that flames shone from trees which were not on fire,
that snakes embraced and flowed around the trunks.
That place the people do not visit with worship near at hand
but leave it to the gods: when Phoebus is in mid-sky
or black night commands the heavens, even the priest dreads
to approach and fears to surprise the master of the grove.

- Lucan. Pharsalia. 399-428.