Born in Bucharest, he lived for part of his childhood at the family manor in Botoşani, where, at age 11, he witnessed first-hand the 1907 peasants' uprisings (which, as he later admitted, contributed to his left-wing sympathies). As a youth, he read Russian anarchist books, while studying in Paris during World War I, joined anarchist circles. While travelling through Finland in 1917, Callimachi attended a public meeting at which Vladimir Lenin gave a speech, and consequently adopted Bolshevism.