Tiw's Beast

First, a real animal exists. Then, it is mythologized. In scriptures and works of fantasy, the myth comes first.

In "Star of the Sea," I, the god Frae rides the bull, Earthshaker, whose bellow makes wells spout and wakes dead kings. Because the bull's might scatters the foe and fructifies the earth, possession of Earthshaker is part of the marriage negotiations between Frae and Niaerdh.

Next, we see a real bull in a historical context but are also told what is believed about it:

"They walked by a paddock where a bull stood, Tiw's beast, his horns mighty beneath the sun."
-7, p. 533.

An incarnation of Earthshaker. He belongs to a different god. Mythology changes. "Star of the Sea" chronicles the changes from Niaerdh, on whose brow shines the morning star, to "Mary, mother of God..." (IV, p. 639), Stella Maris, Star of the Sea. Poul Anderson understands and imaginatively enters each stage of this development.