One feature of especial interest associated with this cemetery is its 197 connexion with an adjacent _arenarium_, or sand pit. This is situated near the basilica of St. Agnes, and overlies part of the Catacomb. It consists of a series of large and gloomy caverns utterly unlike the sepulchral crypts below. A stairway leads down to the Catacomb, and also a deep shaft with foot-holes cut in the rock for climbing. Probably this was the only way of escape in time of persecution. There is also apparent evidence of the existence of a windlass, by which the excavated tufa was raised, and either deposited in the _arenarium_ or carted away. This cemetery has been carefully examined by Padre Marchi, who has published a plan of an area of about seven hundred by five hundred and fifty feet. The united length of the passages in this part is about two English miles. Yet Father Marchi says this area is only about one eighth of the whole Catacomb, the aggregate extent of whose streets would, therefore, be fifteen or sixteen miles. Just without the Porta Pia on this Nomentan Way, is the little Catacomb of Nicodemus. At the third mile, we read in ancient records, was that of Ostrianus or Fons Petri, as it was called, from a tradition that Peter once baptized there. It has not, however, been satisfactorily identified. Nearly six miles from the city is the so-called Catacomb of Alexander, bishop of Rome A. D. 117-120, who, according to the _Liber Pontificalis_, suffered martyrdom by decapitation on this spot under the emperor Hadrian, together with the presbyter Eventius and the deacon Theodulus. Here were discovered in 1853, below the level of the Campagna, the ruins of an ancient basilica erected in honour of these martyrs. In the roofless structure was found a sarcophagus bearing the name of Alexander, and probably once containing his ashes. The graves here are less disturbed than in the Catacombs nearer Rome. This cemetery was used for sepulture 198 comparatively late, as the language of some of the inscriptions indicates a decided approximation to modern Italian. In 1857 the foundations of a large church, designed to include the whole of the ancient structure, were laid with great pomp by the present pontiff.