Albert Einstein came very close to the final form of the equations describing the gravitational field during his collaboration with Marcel Grossmann a fecund period which began in August 1912 and lasted nine months. Nevertheless, the theory published in their joint paper1 showed an "ugly dark spot," as Einstein wrote to Lorentz2 : contrary to initial expectations, the field equations were not generally covariant. Einstein struggled hard to iron out what he considered a major flaw, and eventually succeeded in November 1915, when he presented the final version of his general theory of relativity in a number of communications to the Prussian Academy of Science. Accepted reconstructions of the genesis of the Entwurf paper generally take in the following steps: Einstein & Grossmann initially made the right choice, taking the Ricci tensor into account as the gravitational field tensor, but rejected it later in the paper due to the difficulties encountered in recovering the Newtonian limit in the case of a weak and static gravitational field, making do with equations which were covariant with respect to linear transformations of coordinates. Moreover, in a paragraph entitled "Remarks," added at the end of the Mathematical part (the paper has a "Physical part" and a "Mathematical part," written by Einstein and Grossmann, respectively), Einstein gave what he believed was a proof that all generally covariant equations for the gravitational field were physically unacceptable. Interpretation of the way Einstein accounted for his failure to obtain the correct Newtonian limit and for the limited covariance of the equations is still a moot point among historians of physics. Some believe that Einstein's difficulties were of an essentially mathematical nature, while others stress their physical nature, viewed in terms of Einstein's conception of static gravitational fields as it stood in 1912.