There’s an old myth about vampires / revenants / the like. They cannot cross running water. It may be a reference to the purifying, baptising effect of fresh water; it may also have been a reference to the Styx, or other “rivers of the dead,” over which these creatures will not, or cannot, cross to their salvation.
We cannot go back. The living cannot pass
Where they have travelled: we cannot haunt that path.
We move on, east to west, and sunfire dies.
But vampires sleep in soil and memories:
For them, the flow of life itself is haunted:
The undead cannot cross over flowing waters.