  Within the Euclidean effective action approach we propose criteria for the
ground state of QCD. Despite a nonvanishing field strength the ground state
should be invariant with respect to modified Poincar\'e transformations
consisting of a combination of translations and rotations with suitable gauge
transformations. We have found candidate states for QCD with four or more
colours. The formation of gluon condensates shows similarities with the Higgs
phenomenon.
