Context : A2163 is among the richest and most distant Abell clusters , with outstanding properties in different wavelength domains .
X-ray observations have revealed a distorted morphology of the gaz and strong features have been detected in the temperature map , suggesting that merging processes are important in this cluster .
However , the merging scenario is not yet well–defined .

Aims : We therefore undertook a complementary optical analysis , aiming to understand the dynamics of the system , to constrain the merging scenario and to test its effect on the properties of galaxies .

Methods : We present a detailed optical analysis of A2163 based on new multicolor wide–field imaging and the medium–to–high resolution spectroscopy of galaxies .

Results : The projected galaxy density distribution shows strong subclustering with two dominant structures : a main central component ( A ) , and a northern component ( B ) , visible both in optical and in X-ray , while other substructures are detected in the optical .
At magnitudes fainter than R=19 , the galaxy distribution shows a clear elongation approximately on the east–west axis extending over ~ { } 4 h _ { 70 } ^ { -1 } Mpc , while a nearly perpendicular bridge of galaxies along the north–south axis appears to connect ( B ) to ( A ) .
The ( A ) component shows a bimodal morphology , and the positions of its two density peaks depend on galaxy luminosity : when going to magnitudes fainter than R = 19 , the axis joining the peaks shows a counterclockwise rotation ( from NE/SW to E–W ) centered on the position of the X-ray maximum .
Our final spectroscopic catalog of 512 objects includes 476 new galaxy redshifts .
We have identified 361 galaxies as cluster members ; among them , 326 have high precision redshift measurements , which allow us to perform a detailed dynamical analysis of unprecedented accuracy .
The cluster mean redshift and velocity dispersion are respectively z = 0.2005 \pm 0.0003 and 1434 \pm 60 km/s .
We spectroscopically confirm that the northern and western components ( A2163-B and A2163-C ) belong to the A2163 complex .
The velocity distribution shows multi-modality , with a bimodal structure peaking at \sim 59200 km/s and \sim 60500 km/s .
A significant velocity gradient ( \sim 1250 km/s ) is detected along the NE/SW axis of the cluster , which partially explains the detected bimodality .
A2163 appears to be exceptionally massive : the cluster virial mass is M _ { vir } = 3.8 \pm 0.4 \times 10 ^ { 15 } M _ { \odot } h _ { 70 } ^ { -1 } .

Conclusions : Our analysis of the optical data , combined with the available information from X-ray observations and predictions of numerical simulations , supports a scenario in which A2163-A has undergone a recent ( t \sim 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 .