  We demonstrate the existence of an insulating phase in the three-legged
Hubbard ladder at two-thirds filling. In this phase chargons are bound because
the physics within a unit cell favors the formation of triplets. The resultant
moments lead to a ground state in the Haldane phase, a symmetry protected
topological state of matter. In this purely fermionic model, reflection is
protecting but time reversal and dihedral symmetries are not, in contrast to
spin models.
