  We demonstrate that the electronic spectrum of graphene in a one-dimensional
periodic potential will develop a Landau level spectrum when the potential
magnitude varies slowly in space. The effect is related to extra Dirac points
generated by the potential whose positions are sensitive to its magnitude. We
develop an effective theory that exploits a chiral symmetry in the Dirac
Hamiltonian description with a superlattice potential, to show that the low
energy theory contains an effective magnetic field. Numerical diagonalization
of the Dirac equation confirms the presence of Landau levels. Possible
consequences for transport are discussed.
