Costantini created portraits of writers and artists for newspapers, and illustrated several novels. His early works were inspired by the novelist Franz Kafka, and by literary, utopian and anarchist ideals. His later work presented a pessimistic view of civilization.
His last series offered a dark reading of Pinocchio, which he considered one of the three or four greatest Italian novels. As a child, he was crafty, and kept a diary accompanied with newspaper cut-outs, collages, photos and drawings. At a renowned Roman high school, he failed French and Latin.
World War II
Costantini's experiences during World War II led his focus to the suffering and meaninglessness of the world. It was at this time, too, that he became interested in utopianism. He graduated as sea captain, served in the Italian Navy, and 1951 to 1954 was employed in the Merchant Marine.
He moved with his family to Rapallo and in 1959, after a visit to Spain, devoted a series of paintings to bullfighting. Other members were Eugenio Carmi, Emanuele Luzzati, Carlo Vita, etc. A collector of old illustrated magazines, he used this material to create in his Rapallo home and studio paintings and portraits, which typically include period pieces and advertisements.
He often depicted scenes in Genoa (squares, shops, buildings, boats), contrasting the old and the new. Philip Levine's poem "On a Drawing by Flavio", describes Costantini's stark portrait of the Rabbi of Auschwitz, who "bows his head and prays / for us all". Costantini died in Genoa after a short illness.
He first experimented with illustration after his time spent in the Italian navy doing drawings of Kafka's work. "His earliest ventures into art were motivated more by intellectual frustration than by artistic masters. 'I started to draw because I read the Kafka books… it was impossible to write like Kafka, so I began to draw'.
The Pony by Vladimir Mayakovsky (1969, reprint 2006)
Heart by Edmondo De Amicis (1977)
The Shadow Line by Joseph Conrad (1989).
He was a member of the artists' group that founded the Galleria del Deposito in Boccadasse, Genoa.