 In Einstein’s hands the principle of general covariance was a crucial postulate in the development of  GTR.[11]  The diffeomorphism freedom of GTR, i.e., the invariance of the form of the laws under transformations of the coordinates depending smoothly on arbitrary functions of space and time, is a “local” spacetime symmetry, in contrast to the “global” spacetime symmetries of STR (which depend instead on constant parameters). For a discussion of coordinate-based approaches to the diffeomorphism invariance of General Relativity, see Wallace (forthcoming), and for more on the physical interpretation of this invariance, see Pooley (2017). Such local symmetries are “dynamical” symmetries in Wigner’s sense, since they describe a particular interaction, in this case gravity. As is well known, the spacetime metric in GTR is no longer a “background” field or an “absolute object”, but instead it is a dynamical player, the gravitational field manifesting itself as spacetime curvature.