 The area now covered by the Vatican City had been a cemetery for some years before the Circus of Nero was built.It was a burial ground for the numerous executions in the Circus and contained many Christian burials, because for many years after the burial of Saint Peter many Christians chose to be buried near Peter.In 1939, in the reign of Pope Pius XII, 10 years of archeological research began under the crypt of the basilica in an area inaccessible since the 9th century.