 Alfonso Castaldo was born in Casoria to Aniello Castaldo (d. circa 1897) and Marianna Crispino.The third of five children, he was baptized in his home four days later, on 10 November, by his paternal uncle, who was a canon by the same name, with the permission of the Naples curia.Castaldo, influenced by Monsignor Francesco Morano and Father Luigi Maglione, decided to pursue a career in the Church, and attended the seminaries in Cerreto Sannita, Pozzuoli, and Naples.