Born in Rome on March 7, 1877,[2] Caetani graduated from the Columbia University School of Mines in 1903.

[3] He dug gold in Idaho and filled several other mining contracts before founding the firm of Caetani, Burch & Hershey in San Francisco.

When Italy entered the First World War, he returned home and joined the Italian army engineers.

In April 1916 he led a successful tunnelling attack on an Austro-Hungarian stronghold on top of Col di Lana.

Promoted to colonel by the end of the war, Gelasio Caetani won three decorations for bravery.