The postal building (1933-35) is one of the main Roman examples of Rationalism, an international movement centred on the exigency of order and logic, whose architectural style results from the application of rationality and from a perfect correspondence between the building and its function. According to Le Corbusier «the postal office of Testaccio is Roman, but charged with modern formalism».
The architect is Adalberto Libera (1903-1963), born in Trento but Roman by adoption, founder of the Group 7 in 1926 and soul of the Movimento Italiano di Architettura Razionale (Italian Movement of Rational Architecture – MIAR), of which he organized the first two expositions in Rome (1928, 1931). Libera also made the Palazzo dei Congressi in EUR (1937-1942), and Villa Malaparte in Capri (1938-40). He collaborated, also for other projects, with the Roman architect Mario De Renzi  (1897-1967). In 1933 Libera and De Renzi were awarded the first prize in a competition organised by the Ministero delle Poste (Postal Service Ministry) in order to entrust the building of four postal edifices (the others are in Via Taranto, piazza Bologna, and Viale Mazzini).

These buildings as a whole are amongst the finest examples of the architecture of the time in Rome.

The building, placed on top of a wide flight of steps, like a classical monument, and built along the East-West axe, has a rigorous symmetrical composition, based on geometric connections and on the golden section.
The building, showing in its exteriors in smooth marble a unitary symmetry, is articulated in three volumes which mark clearly their distinct functions. One is the U-shaped building body with three floors housing offices, which is divided in its turn into the double height central space for distributing the mail – marked on the back front by the thick grid of squared holes – and into the side zones destined to the floors with the offices.
Then are the terminal elements, showing a typical motive of intersecting diagonals which reveal the stairway body.
Finally, the lower body includes the hall for the public and a glass tambour overlooking the exterior.
A portico connects the building bodies, thus closing the squared court around which the composition is build.

(F. Riccio).