Synonyms for Fort (same or very similar meaning)
WordNet sense 1 (a fortified military post where troops are stationed):
garrisonWordNet sense 2 (a fortified defensive structure):
fortressWordNet sense 3 (gather in, or as if in, a fort, as for protection or defense):
fort upWordNet sense 4 (enclose by or as if by a fortification):
fortifyFrom the ODE community, based on WordNetadd/edit