  The interaction of Galactic-Centre (GC) super bubbles (GSB) with the gaseous
disc and halo of the Milky Way is investigated using radio continuum, X-ray, HI
and CO line surveys. The radio North Polar Spur (NPS) constitutes the brightest
eastern ridge of GSB, brightening towards the galactic plane and reaching $ l =
22\deg, \ b = + 2\deg$ at the sharpest end, where it intersects the tangential
direction of the 3-kpc expanding ring and crater. Examination of the spur
ridges reveals that the entire GSB, including the NPS and its counter spurs,
constitutes a GC-symmetrical $\Omega /$\rotatebox[origin=c]{180}{$\Omega$}
shape. The thickness and gas density of the HI and CO discs are shown to
increase sharply from the inside (lower longitude) to the outside of the 3-kpc
crater. Formation of crater is explained by the sweeping of the upper layer of
disc gas by the shock wave from the GC by the explosion $ \sim 10 $ My ago with
the emitted energy of several $10 ^ {55} $ ergs. Based on the discussion, a
unified view on the structure and formation mechanism of GSB is presented.

Astrophysics of Galaxies