In many respects, the year 1916 marks the beginning of the development of GTR as an autonomous, mature discipline, with its own research agenda and open problems actively pursued by leading physicists and mathematicians. In January, Einstein was still diffident about his own ability to write a review article for the physics community at large, covering the latest developments in the field. He even suggested to Lorentz that he undertake such a task instead.² Justs two months later he was already sending Wilhelm Wien, then editor of the Annalen der Physik, his manuscript of an overview presentation of the theory, including adapted versions of the third and fourth Academy communications. This review was published in the Annalen in May 1916 and later reprinted as a separate booklet.³ At the same time,⁴ Einstein had also been thinking about a popular book on special and general relativity that appeared in the spring of 1917; it quickly became a classic, undergoing many editions, translations and reprints.⁵ Still, many important, basic aspects of the theory were yet to be worked out, assimilated and refined by Einstein and his colleagues. It took considerable time before this task would be accomplished to a reasonable degree.⁶