Why the mathematics bears this power of "dragging along" in physics theories? It looks that certain mathematical structures are more convenient to physics than other ones, which seems to evidence the presence of some dissimulated physical content in certain mathematical theories. In the case of General Relativity, these mathematical concepts seem to be the ones of continuous surface (or curvature, in a general form) – already foreseen by Gauss and Riemann, who searched for an effective space geometry – and, lastly, invariant, which allowed to express general covariance in an non-equivocal way, by means of tensional calculus. The path stepped by physics in the early 20^th century allowed finding the answer to the question made by Gauss and Riemann about space structure.