  Cylindrically reduced Einstein gravity can be regarded as an $SL(2,R)/SO(2)$
sigma model coupled to 2D dilaton gravity. By using the corresponding 2D
diffeomorphism algebra of constraints and the asymptotic behaviour of the Ernst
equation we show that the theory can be mapped by a canonical transformation
into a set of free fields with a Minkowskian target space. We briefly discuss
the quantization in terms of these free-field variables, which is considerably
simpler than in the other approaches.
