Toward the middle of the third century, as we have seen, even the 174 cemeteries themselves were not secure from invasion by the persecuting tyrants. When the protection of the law was withdrawn, the public stairways A and B, Fig. 26, were blocked up and partially destroyed, new passages, B2 and B3, were opened into the adjacent _arenarium_ for the entrance and escape of the Christians, and a very narrow and steep secret stairway, X4, was constructed from the roof of the latter to the open air, requiring a ladder, which might be removed to cut off pursuit, or the assistance of friends for entrance or departure.[302] We have here an affecting instance of the perils to which the persecuted Christians were exposed when hunted through these gloomy crypts by their cruel pagan foes. The difference between the straight and narrow galleries of the Catacombs and the wide and unsymmetrical windings of the _arenarium_ will be remarked. Connexions were also formed with adjacent areas at S, C1, C2, and B1, sometimes breaking directly through the _loculi_ and _cubicula_. The utmost economy of space was now observed, every available foot of wall being occupied; the inscriptions become more rude, indicating poverty and oppression; and the stucco or marble ornaments give place to rude carvings of the tufa itself into cornices, columns, and capitals. Some of the _cubicula_ are made of larger size, as if for worship, sometimes six or eight-sided, and occasionally with apsidal recesses. During the terrible period of the Diocletian persecution, when the cemeteries were confiscated by the heathen government, the Christians, in order to prevent the profanation of the more sacred sepulchres, and especially that of the bishops, filled up the principal galleries with earth at immense expense and labour. Much of this still encumbers the 175 passages and forms the chief obstacle to their exploration. On the cessation of the persecution some of these galleries leading to the principal crypts were cleared out by means of cylindrical shafts made for the purpose; and sometimes new galleries were excavated in the tufa above the old ones, the floor of which was formed of the consolidated earth in the former gallery. Where this earth has been removed the height of the two galleries is, in places, twenty feet, filled with graves to the top, the upper part being much narrower than the lower. The obstructions in the stairways A and B were also removed and the stairs renewed.