  Pure three-dimensional gravity in anti-de Sitter space can be formulated as
an SL(2,R) $\times $ SL(2,R) Chern-Simons theory, and the latter can be reduced
to a WZW theory at the boundary. In this paper we show that AdS$_3$ gravity
with free boundary conditions is described by a string at the boundary whose
target spacetime is also AdS$_3$. While boundary conditions in the standard
construction of Coussaert, Henneaux, and van Driel are enforced through
constraints on the WZW currents, we find that free boundary conditions are
partially enforced through the string Virasoro constraints.
