威尼斯省
Mandić grew up in the orbit of a community of Capuchin friars based in the Province of Venice who had served in his town for two centuries, dating from when the area was ruled by the Republic of Venice. Physically malformed and delicate, he grew to a height of only 1.35 m (4'5"), with a clumsy walk. He also had a stutter. Having felt called to follow that way of life, in November 1882, when he was 16, he went to Udine to enter the minor seminary of the Capuchin Venetian Province. Two years later he was admitted to the friars' novitiate in Bassano del Grappa, where he was clothed in the Capuchin habit and given the religious name of Leopold of Castelnuovo. On 3 May 1885, he made his first profession of religious vows, after which he was sent to pursue his studies for Holy Orders in Capuchin friaries in Padua and Venice. He made his profession of perpetual vows in 1888.