The child of an unknown Venetian nobleman and a prostitute, Rosa grew up on her own in the streets of Venice. In 1475, she attempted to pickpocket the leader of the Venetian Thieves Guild and was caught red-handed. But, Antonio, instead of reporting her to the police, took her on as a pupil. He kept several logs of her training, noting that her ability to leap up from the street to seemingly unreachable windowsills "was unprecedented".