  We present a detailed optical analysis of the galaxy cluster A2163 based on
new multicolor wide field imaging and medium-to-high resolution (R~2000)
spectroscopy. While X-ray observations have revealed that merging processes are
present in this cluster, the merging scenario is complex and not well-defined.
We undertook a complementary optical analysis, aiming to understand the
dynamics of the system, to add constraints to the merging scenario and to test
its effect on the properties of galaxies. We provide a spectroscopic catalog of
512 new objects, where 361 galaxies are identified as cluster members. We
derived estimates of the mean redshift and velocity dispersion: z= 0.2005 +/-
0.0003 and 1434 +/- 60 km/s, and performed a detailed dynamical analysis of
unprecedented accuracy. We detected multiple evidences of merging events: i)
strong subclustering in the galaxy density distribution, showing a main central
component A2163-A, a northern one A2163-B, visible both in optical and in
X-ray, and other substructures detected in optical, ii) bimodality in the
density distribution for A2163-A, strong segregation between gaz and galaxies,
and between galaxies of different luminosities, iii) low-density structures
oriented along specific axes: mainly the EW direction, and the NS one,
embedding the main substructures, iv) bimodality in the velocity distribution
and a velocity gradient (~1250 km/s) along the NE/SW axis of the cluster. A2163
is exceptionally massive, with Mvir = 3.8 +/- 0.4 10**15 Msol/h70. Our analysis
supports a scenario in which A2163-A has undergone a recent (t ~ 0.5 Gyr)
merger along a a NE/SW (or E--W) axis, and A2163-B is connected to the main
complex, probably infalling on A2163-A. (abridged)
