  The structure of supergiant shells, in particular of LMC 4, is hard to
explain with stochastic self-propagating star formation. A series of supergiant
structures lies along the outer edge of the LMC and form a sequence increasing
clockwise in age. We have considered the rotation of the LMC and its motion
through the halo of the Milky Way and propose that these structures find their
origin in star formation induced in the bow-shock formed at the leading edge of
the LMC. Due to the rotation of the LMC these structures then move aside.
