  Einstein gravity in both 3 and 4 dimensions, as well as some interesting
generalizations, can be written as gauge theories in which the connection is a
Cartan connection for geometry modeled on a symmetric space. The relevant
models in 3 dimensions include Einstein gravity in Chern-Simons form, as well
as a new formulation of topologically massive gravity, with arbitrary
cosmological constant, as a single constrained Chern-Simons action. In 4
dimensions the main model of interest is MacDowell-Mansouri gravity,
generalized to include the Immirzi parameter in a natural way. I formulate
these theories in Cartan geometric language, emphasizing also the role played
by the symmetric space structure of the model. I also explain how, from the
perspective of these Cartan-geometric formulations, both the topological mass
in 3d and the Immirzi parameter in 4d are the result of non-simplicity of the
Lorentz Lie algebra so(3,1) and its relatives. Finally, I suggest how the
language of Cartan geometry provides a guiding principle for elegantly
reformulating any 'gauge theory of geometry'.
