  We report the discovery of a potentially major supercluster that extends
across the Galactic Plane in the constellation of Vela, at a mean recessional
velocity of ~18,000 km/s. Recent multi-object spectroscopic observations of
this Vela Supercluster (VSCL), using AAOmega+2dF and the Southern African Large
Telescope, confirm an extended galaxy overdensity in the Zone of Avoidance
(ZOA) located where residual bulk flows predict a considerable mass excess. We
present a preliminary analysis of ~4,500 new spectroscopic galaxy redshifts
obtained in the ZOA centred on the Vela region (l=272.5+-20 deg, b=0+-10 deg).
The presently sparsely-sampled dataset traces an overdensity that covers 25 deg
in Galactic longitude on either side of the Plane, suggesting an extent of 25
deg x 20 deg, corresponding to ~115 x 90 $h_{70}$ Mpc at the supercluster
redshift. In redshift space, the overdensity appears to consist of two merging
wall-like structures, interspersed with clusters and groups. Both the velocity
histogram and the morphology of the multi-branching wall structure are
consistent with a supercluster classification. $K_s^o$ galaxy counts show an
enhancement of ~1.2 over the survey area for galaxies brighter than $M_K^*$ at
the VSCL distance, and a galaxy overdensity of $\delta=0.50\rm{-}0.77$ within a
photometric redshift shell around the VSCL, when compared to various Two-Micron
All-Sky Survey samples. Taking account of selection effects, the VSCL is
estimated to contribute $v_\rm{LG} \gtrsim 50$ km/s to the motion of the Local
Group.
