Grani Weight

Now Sigurđ ate a part of the dragon’s heart, and kept another part
of it. Then he mounted up on his horse Grani and followed Fáfnir’s
tracks to his lair and found it open, and its doors were made of iron, as
were the doorframes and all the pillars in the house, and they were dug
deep into the earth. Sigurđ found a great quantity of gold there and the
sword Hrotti, and he took the terror-helmet and a golden suit of armor
and many other precious treasures. He found so much gold there that
he thought even two or three horses would hardly be enough to carry it.
He took all the gold and put it into two large chests, and then he took
his horse Grani by the bridle to walk him. The horse would not move
and would not be driven along. Then Sigurđ thought he knew what the
horse wanted. He leapt on Grani’s back and struck him with his spurs,
and then the horse ran as if he carried nothing at all.


- Volsunga Saga, Chapter 20