  A number of recent works in E-print arXiv have addressed the foundation of
gauge gravitation theory again. As is well known, differential geometry of
fibre bundles provides the adequate mathematical formulation of classical field
theory, including gauge theory on principal bundles. Gauge gravitation theory
is formulated on the natural bundles over a world manifold whose structure
group is reducible to the Lorentz group. It is the metric-affine gravitation
theory where a metric (tetrad) gravitational field is a Higgs field.
