Amphiphilic proteins and peptides can induce the formation of stable and metastable pores in membranes. Using coarse-grained simulations, we have studied the factors that affect structure of peptide-stabilized pores. Our simulations are able to reproduce the formation of the well-known barrel-stave or toroidal pores, but in addition, we find evidence for a novel "double-belt" pore structure: in this structure the peptides that coat the membrane pore are oriented parallel to the membrane plane. To check the predictions of our coarse-grained model, we have performed more detailed simulations, using the MARTINI force field. These simulations show that the double-belt structure is stable up to at least the microsecond time scale.