  A new semianalytical model that explains the formation and sizes of the
'great walls' - the largest structures observed in the universe is suggested.
Although the basis of the model is the Zel'dovich approximation it has been
used in a new way very different from the previous studies. Instead of
traditional approach that evaluates the nonlinear density field it has been
utilized for identification of the regions in Lagrangian space that after the
mapping to real or redshift space (depending on the kind of structure is
studied) end up in the regions where shell-crossing occurs. The set of these
regions in Lagrangian space form the progenitor of the structure and after the
mapping it determines the pattern of the structure in real or redshift space.
The particle trajectories have crossed in such regions and the mapping is no
longer unique there. The progenitor after mapping makes only one stream in the
multi-stream flow regions therefore it does not comprise all the mass.
Nevertheless, it approximately retains the shape of the structure. The
progenitor of the structure in redshift space depends on a few non-Gaussian
fields and also it is strongly affected by two anisotropic fields that
determine the pattern of great walls as well as their huge sizes. All the
fields used in the mappings are derived from the linear potential smoothed at
the current scale of nonlinearity which is $R_{nl} = 2.7$ {\hmpc} for the
adopted parameters of the \lcdm universe normalized to $\sigma_8 = 0.8$. The
model predicts the existence of walls with sizes significantly greater than 500
{\hmpc} that may be found in sufficiently large redshift surveys.
