Full Idea
Something which is established in the centre and has equality in relation to the extremes has no more reason to move up than it has down or to the sides (so the earth is stationary)
Gist of Idea
The earth is stationary, because it is in the centre, and has no more reason to move one way than another
Source
report of Anaximander (fragments/reports [c.570 BCE], A26) by Aristotle - On the Heavens 295b11
Book Reference
'The First Philosophers', ed/tr. Waterfield,Robin [OUP 2000], p.16