X-ray galaxy clusters are ideal tracers of the large-scale structure of the Universe .
Based on the ROSAT All-Sky Survey we are constructing a sample of the X-ray brightest galaxy clusters for cosmological studies .
We have already completed the compilation of a sample of about 1000 clusters in the sky excluding a 40 degree wide band around the galactic plane .
We have demonstrated with the southern sample , which is the so far most complete , that we can get reliable statistical measures of the large-scale structure of the Universe to scales in excess of 400 h ^ { -1 } Mpc .
With the experience gained in these projects we are extending the search for X-ray galaxy clusters into the Zone-of-Avoidance .
We have compiled a sample of 181 good cluster candidates with a well defined completeness of about 70 % down to a flux limit of 3 \cdot 10 ^ { -12 } erg s ^ { -1 } in the zone with an absorption depth of A _ { v } \leq 2.25 .
The candidates are definitely identified and redshifts are obtained in an ongoing optical follow-up program .