We conduct an intensive study of the rich, X--ray
luminous, and hot galaxy cluster Abell 697 (at $z=0.282$), likely
containing a diffuse radio--emission, to determine its dynamical
status.

Our analysis is based on new spectroscopic data obtained at
the TNG telescope for 93 galaxies and on new photometric data obtained
at the INT telescope in a large field. We combine galaxy velocity and
position information to select 68 cluster members (out to $\sim 1.3$
\h from the cD galaxy), determine global dynamical properties, and
detect possible substructures. The investigation of the dynamical
status is also performed by using X--ray data stored in the Chandra
archive.

We compute the line--of--sight (LOS) velocity dispersion of
galaxies, $\sigma_{\rm v}=1334_{-95}^{+114}$ \kss, in agreement with
the high average X--ray temperature $T_{\rm X}=$(10.2$\pm$0.8) keV
recovered from Chandra data, as expected in the case of
energy--density equipartition between galaxies and gas. Assuming that
the cluster is in dynamical equilibrium and mass follows the galaxy
distribution, we find that A697 is a very massive cluster obtaining
$M(<{\rm R}_{\rm max}=0.75$ \hh)$=9.5^{+1.8}_{-1.5}$ \mqua and
$M(<{\rm R}_{\rm vir}=3.85$ \hh)$=4.5_{-1.3}^{+1.4}$ \mqui for the
region well sampled by the spectroscopic data and for the entire
virialized region, respectively. Further investigations find that
A697 is not fully relaxed, as shown by the non Gaussianity of the
velocity distribution, the elongation of the X--ray emission, and the
presence of small-size substructures in the central region.

Our results suggest that we are looking at a cluster undergone to a
complex cluster merger occurring roughly mainly along the LOS, with a
transverse component in the SSE--NNW direction. The importance and the
phase of the merging event is discussed. The spatial correlation
between the (likely) radio halo and the optical and X--ray cluster
structure supports the hypothesis of a relation between extended radio
emission and merging phenomena.