  Superclusters are the largest relatively isolated systems in the cosmic web.
Using the SDSS BOSS survey we search for the largest superclusters in the
redshift range $0.43<z<0.71$.
  We generate a luminosity-density field smoothed over $8 h^{-1}\mathrm{Mpc}$
to detect the large-scale over-density regions. Each individual over-density
region is defined as single supercluster in the survey. We define the
superclusters in the way that they are comparable with the superclusters found
in the SDSS main survey.
  We found a system we call the BOSS Great Wall (BGW), which consists of two
walls with diameters 186 and 173 $h^{-1}$Mpc, and two other major superclusters
with diameters of 64 and 91 $h^{-1}$Mpc. As a whole, this system consists of
830 galaxies with the mean redshift 0.47. We estimate the total mass to be
approximately $2\times10^{17}h^{-1}M_\odot$. The morphology of the
superclusters in the BGW system is similar to the morphology of the
superclusters in the Sloan Great Wall region.
  The BGW is one of the most extended and massive system of superclusters yet
found in the Universe.
