  The purpose of this paper is to show how to obtain the mass of a unimodular
lattice from the point of view of the Bruhat-Tits theory. This is achieved by
relating the local stabilizer of the lattice to a maximal parahoric subgroup of
the special orthogonal group, and appealing to an explicit mass formula for
parahoric subgroups developed by Gan, Hanke and Yu.
  Of course, the exact mass formula for positive defined unimodular lattices is
well-known. Moreover, the exact formula for lattices of signature (1,n) (which
give rise to hyperbolic orbifolds) was obtained by Ratcliffe and Tschantz,
starting from the fundamental work of Siegel. Our approach works uniformly for
the lattices of arbitrary signature (r,s) and hopefully gives a more conceptual
way of deriving the above known results.
