Fortresses rhymes with:
actress's, actresses, mattress's, waitresses, actress's, actresses, choruses, congress', congress's, congresses, cypress's, embarrasses, gavras's, heiresses, irises, mattress's, norris's, retroviruses, sampras's, virus's, waitresses, walruses
Fortresses sounds like:
fortier's, fortress, forwarders, frederic, frederica, frederick, frederick's, fredericka, fredericks, frederico, frederika, fredric, fredrich, fredrick, fredricks, fridrich, friederich, friederike, friedrich, friedrichs, friedrick, furthers