In 1937, the Mussolini regime decided it was time for a new central-Rome railroad station. It was to be ready in time for E42, an enormous fair with permanent buildings in what is now EUR, all designed to celebrate the 20th anniversary of the March on Rome. The war intervened, Mussolini was thrown out of power in 1943, and construction stopped on both E42 and the new Termini Station. The station's enormous side structures, designed by Angiolo Mazzoni del Grande, had been completed, and these remain.
The rest of the building was subject to a 1947 design competition. Two teams emerged victorious--nobody really famous among them--and together they re-imagined the structure, which was inaugurated in 1950.
Inside, the great hall was covered by a concrete roof, which one source describes as a modernist version of the barrel vaults used in ancient Roman baths. This roof is integrated with a cantilevered canopy over the entrance. Spectacular, we think. The station was, and is, one of the largest in Europe.
The postcard view shown here captures the modernist allure of the Stazione Termini in its first decade. The automobiles offer the possibility of a more precise dating, but we're not car buffs, and to be reasonable accurate, one would have to identify the newest car in the lots. Not easy. Still, perhaps a reader can help date the photo more precisely. [See the wonderfully detailed comment below from Roger H. who identifies a couple cars and concludes the photo was taken close to when station was inaugurated.]
A few postscripts from Dianne:
The piazza is no longer called "Piazzale della Stazione," as we see in the postcard photo above, but "Piazza dei Cinquecento" ("Piazza of the 16th century") - I assume that's the meaning, and not the piazza of the Fiat car, the 500 (i.e. cinquecento). [CORRECTION - Nope, that's not its meaning. I should've known it would've been political and more serious. Both Marco and Frederika pointed out the real meaning of the cinquecento - Italians soldiers killed in Ethiopia. See their helpful comments below.] The national train service has a rather thorough, if somewhat glorified, history of the station on its Web site. (You'll get some different opinions about it on Yelp.) And the station, because of its roof line, is sometimes called the Dinosaur.