Read "Of Those Sentiments Concerning Nature with Which Philosophers Were Delighted" by Plutarch online for free on Textopian. Full text with search, annotations, highlights, and AI-powered reading aids.
The Stoics believe that it is of the same figure with the sun, spherical. Empedocles, that the figure of it resembles a quoit. Heraclitus, a boat. Others, a cylinder.