Many late antique and medieval sources show that the Early Christian basilica of Saint Peter's had a baptistery, but it has left no physical traces. Early descriptions of the location of this inscription are particularly interesting. Until the fifteenth century, the inscription was not inside the basilica but outside, fixed on the external wall near the hillside. The idea that the baptistery of Saint Peter's was monumental and independent was developed some time ago by Gillian Mackie. Many observations seem to indicate that the baptistery of Saint Peter's was a monumental one. It remains certain that the place of the Vatican baptistery must be associated with the north transept where it was described from the sixth-century Gesta Liberii to Alfarano a thousand years later, but the exact place indicated on Alfarano's plan was probably only the vestibule of an external independent and monumental baptistery.