  For an integer $n\geq 1$, we display a poset $\Phi_n$ whose maximal chains
are in bijection with the $n\times n$ alternating sign matrices. The Hasse
diagram $\widehat \Phi_n$ is obtained from the $n$-cube by adding some edges.
We show that the dihedral group $D_{2n}$ acts on $\widehat \Phi_n$ as a group
of automorphisms.
