Midgard

Then spoke Gangleri: ‘This is important information that I
have just heard. That is an amazingly large construction and
skilfully made. How was the earth arranged?’

Then High replied: ‘It is circular round the edge, and around it
lies the deep sea, and along the shore of this sea they gave lands to
live in to the races of giants. But on the earth on the inner side they
made a fortification round the world against the hostility of
giants, and for this fortification they used the giant Ymir’s
eyelashes, and they called the fortification Midgard. They also
took his brains and threw them into the sky and made out of them
the clouds, as it says here:

From Ymir’s flesh was earth created, and from blood, sea;
rocks of bones, trees of hair, and from his skull, the sky.

And from his eyelashes the joyous gods made Midgard for
men’s sons, and from his brains were those cruel clouds all
created.’


- Prose Edda, Gylfaginning