He is most famed for Il Plastico, a massive scale model of imperial Rome under Constantine the Great.
Gismondi entered the Amministrazione delle Antichità e Belle Arti in 1910 and was named Director of the Ostia excavations where he remained for 44 years.
[1] A trained architect, he carried out numerous projects, including a plan of the Imperial forums in Rome in 1933; the restoration of the northwest portion of the Baths of Diocletian (1927) and also work on the Planetarium of the same complex.
The model is generally built on a scale of 1:250 but somewhat enlarges the more important buildings to allow greater detail work.
Commissioned by Benito Mussolini in 1933 in honor of the 2000th anniversary of Augustus's birth, it is principally based on Lanciani's edition of the 3rd-century Severan Forma Urbis Romae but incorporates other archaeological work and extends it to represent the city under Constantine the Great in the early 4th century.