In mathematics, a Niemeier lattice is one of the 24 positive definite even unimodular lattices of rank 24, which were classified by Hans-Volker Niemeier (1973). Venkov (1978) gave a simplified proof of the classification. Witt (1941) mentions that he found more than 10 such lattices, but gives no further details. One example of a Niemeier lattice is the Leech lattice found in 1967.