  The North Polar Spur (NPS) is the brightest filament of Loop I, a large
circular feature in the radio continuum sky. In this paper, a model consisting
of two synchrotron emitting shells is presented that reproduces large-scale
structures revealed by recent polarization surveys. The polarized emission of
the NPS is reproduced by one of these shells. The other shell, which passes
close to the Sun, gives rise to polarized emission towards the Galactic poles.
It is proposed that X-ray emission seen towards the NPS is produced by
interaction of the two shells. Two OB-associations coincide with the centers of
the shells. A formation scenario of the Loop I region is suggested.
