Full Idea
In the ancient world Plato's Theory of Forms was mostly seen as one aspect of Plato's 'physics' or theory of the world (rather than as 'metaphysics').
Gist of Idea
Plato's Forms were seen as part of physics, rather than of metaphysics
Source
report of Plato (Timaeus [c.362 BCE]) by Julia Annas - Ancient Philosophy: very short introduction Ch.5
Book Reference
Annas,Julia: 'Ancient Philosophy: a very short introduction' [OUP 2000], p.81
A Reaction
This is how I also see the theory, but then I am inclined to see religion as a rather startling branch of speculative physics. Annas cites 'Timaeus' as the key text for this.