If you notices small black spots on the leaves before they turned purple, it's fig rust.
Unless you grow a susceptible variety it's not a serious disease: rake ALL fallen leaves and sispose of them, do not put them in the compost pile and if you have lawn sprinklers set them up so they won't water your fig tree. This should be enough to stop the disease from overwintering: should it happen again or should it become more serious (again: some cultivars are susceptible to it), treat the tree with Daconil. You should find it for sale at Home Depot.
