Looking again at Einstein's "Relativity - The Special and General Theory" I read again his comment at the end of Chapter XVII (Minkowski's Four-Dimensional Space). I wondered what our physicists on the forum would take away from his comment: "These inadequate remarks can give the reader only a vague notion of the important ideas contributed by Minkowski. Without it the general theory of relativity, of which the fundamental ideas are developed in the following pages, would perhaps have got no farther than its long clothes." A couple of questions that come to mind are 1) Could someone have developed general relativity theory without prior thoughts of a Minkowski 4-dimensional space? 2) Were Einsteins' thoughts in the development of general relativity motivated from a picture of a physical 4-dimensional universe, or was it just Minkowski's mathematical formulation?