But standing clear of the fray Achilles’ horses wept
from the time they first had sensed their driver’s death,
brought down in the dust by man-killing Hector.
…But both balked at returning now to the ships
moored at the Hellespont’s far-reaching shore
or galloping back to fight beside the Argives.
Staunch as a pillar planted tall above a barrow,
standing sentry over some lord or lady’s grave-site,
so they stood, holding the blazoned chariot stock-still,
their heads trailing along the ground, warm tears flowing
down from their eyes to wet the earth…the horses mourned,
longing now for their driver, their luxurious manes soiled,
streaming down from the yoke-pads, down along the yoke.

– Homer

The Iliad, Book 17, lines 494-496, 499-508. Although clear of the fighting, Achilles’ immortal horses sense the death of Patroclus and begin to weep and mourn – Achilles himself has yet to learn of the loss of his friend. The horses’ emotional reaction speaks to the close love bond and friendship bond that binds Achilles and Patroclus.