  We reformulate the general theory of relativity in the language of
Riemann-Cartan geometry. We start from the assumption that the space-time can
be described as a non-Riemannian manifold, which, in addition to the metric
field, is endowed with torsion. In this new framework, the gravitational field
is represented not only by the metric, but also by the torsion, which is
completely determined by a geometric scalar field. We show that in this
formulation general relativity has a new kind of invariance, whose invariance
group consists of a set of conformal and gauge transformations, called Cartan
transformations. These involve both the metric tensor and the torsion vector
field, and are similar to the well known Weyl gauge transformations. By making
use of the concept of Cartan gauges, we show that, under Cartan
transformations, the new formalism leads to different pictures of the same
gravitational phenomena. We show that in an arbitrary Cartan gauge general
relativity has the form of a scalar-tensor theory. In this approach, the
Riemann-Cartan geometry appears as the natural geometrical setting of the
general relativity theory when the latter is viewed in an arbitrary Cartan
gauge. We illustrate this fact by looking at the one of the classical tests of
general relativity theory, namely the gravitational spectral shift. Finally, we
extend the concept of space-time symmetry to the more general case of
Riemann-Cartan space-times endowed with scalar torsion. As an example, we
obtain the conservation laws for auto-parallel motion in a static spherically
symmetric vacuum space-time in a Cartan gauge, whose orbits are identical to
Schwarzschild orbits in general relativity.
