hearth [hearths](part of furnace) noun [UK: hɑːθ] [US: ˈhɑːrθ]
melting pot(place where many divergent things come together and are homogenized) noun [UK: ˈmelt.ɪŋ pɒt] [US: ˈmelt.ɪŋ ˈpɑːt]
crisolnoun {m}
crucible [crucibles](cup-shaped piece of laboratory equipment) noun [UK: ˈkruː.sɪb.l̩] [US: ˈkruː.səb.l̩]Cities are the crucibles of civilisation. = Las ciudades son los crisoles de la civilización.