What I've read on special relativity has built it up from its two postulates, the principle of relativity (in the restricted sense) and the constancy of the propagation of light in vacuo. But I haven't seen general relativity's postulates in such a concise listing. I assume the equivalence principle is a postulate required to derive general relativity, as well as the general principle of relativity.. Are these the only two postulates needed for GR? Is the constancy of the propagation of light in vacuo a GR postulate as well, or is it only a postulate of SR? Also, was there a single paper that defined what the general theory of relativity is? Some things I've read have said GR was published in 1915, while most say it was in 1916, and I've read that earlier works relating to GR were also published. Everyone seems to agree that On the Electrodynamics of Moving Bodies, published in the Annalen der Physik, was the paper that defined special relativity, but was there such a paper for general relativity, or was it developed through a series of publications?