Caligula had brought the obelisk from Heliopolis some time during the four short years of his reign and placed it in the circus he began to build in those gardens of his mother, the noble Agrippina the elder, which lay along the northern side of the plain between the Janiculum and Mons Vaticanus. There it stood on the centre of the _spina_, the long, straight line stretching down the middle of the arena from the two opposite goals at either end. Caligula was assassinated before he could finish the circus and it was completed some thirteen years later by Nero, under whom it became the scene of those atrocities against the Christians which have rendered his reign infamous. St. Peter was crucified one year before the death of Nero. His cross was raised on the _spina_ of the circus at an exact distance between the two goals--_metas_--built at either end of the amphitheatre, and therefore, at the foot of the obelisk which stood on that spot. Christian tradition handed down the description of the place “between the two goals” (inter duas metas). Now _meta_ was a name afterward given to tombs of pyramidal shape, two of which existed in mediæval Rome--one, that of Caius Cestius, still standing next to the present Protestant Cemetery, and the other in the Borgo Vecchio, destroyed later by Alexander VI. A straight line drawn from one of these tombs to the other has its centre in a point on the Janiculum, and therefore this spot was thought to be the exact location of St. Peter’s martyrdom. Even to-day visitors to the exquisite Tempietto of Bramante, erected in the cloister of the Church of San Pietro in Montorio, are shown below its pavement the very stone in which the cross of St. Peter was fixed. The legend of this location for the crucifixion of St. Peter grew up during the Middle Ages, a period in which all knowledge of the authentic site was entirely lost. Modern archæology has recently succeeded in locating this position and its topography can now be easily understood.