A sometimes-neglected part of studying Stoicism, is the unitary nature of the school. Even if you discard their beliefs, knowing about them and the attempt at an exhaustive ontology is worth the investment.
Stoic Physics is indebted to the work of Heraclitus, of which we have only fragments today. Heraclitus is known for his development of the Logos from it’s more base meaning of ‘word’ or ‘reason’ to that more specialized connotation of the ‘ordering principle of the cosmos.’
If you haven’t read Heraclitus, the near-mystical quality of the fragments are well-worth the time, I think.
This PDF and others are available at the College’s Library Page if you’re interested:
http://community.middlebury.edu/~harris/Philosophy/heraclitus.pdf
Mountain Stoic 