Family
Peter was the youngest of ten children born to Basil the Elder and Emmelia (Emily) of Caesarea, a wealthy Cappadocian Greek family celebrated for its piety. His maternal grandfather is recorded as a Christian martyr executed in the years before the conversion of Constantine I, and his grandmother, Saint Macrina the Elder, was a follower of Gregory Thaumaturgus.
Four of his siblings are venerated as saints: Saint Basil the Great, Saint Gregory of Nyssa, Saint Macrina the Younger, and Saint Naucratius. The household also included Theosebia the Deaconess. This concentration of sanctity in a single family is among the most striking in the history of the Church.
After their father's death, Peter helped found a monastery together with his mother and sister, the female community at Annesi supervised by Macrina while Peter later headed the corresponding male community.