  By Goldman-Iwahori, the Bruhat-Tits building of the general linear group
$\operatorname{GL}_n$ over a local field $\ell$ can be described as the set of
non-archimedean norms on $\ell^n$. Via a Tannakian formalism, we generalize
this picture to a description of the Bruhat-Tits building of an unramified
reductive group $G$ over $\ell$ as the set of norms on the standard fiber
functor of a special parahoric integral model of $G$. We also give a
moduli-theoretic description of the parahoric group scheme associated to a
point of the building as the group scheme of tensor automorphisms of the
lattice chains defined by the corresponding norm.
