By the end of the fourth century burials in catacombs became rare, and still more between 400 and 410. They were apparently given up altogether after 410. The development of open-air cemeteries increased in proportion, those of S. Lorenzo and S. Paolo fuori le Mura being among the most popular. In 1863, when the entrance-gate to the modern Camposanto adjoining S. Lorenzo was built, fifty tombs, mostly unopened, were found in a space ninety feet long by forty feet wide. Since that time five hundred tombstones have been gathered in the neighborhood of that favorite church. As regards S. Paul's cemetery, more than one thousand inscriptions, whole or in fragments, were found in rebuilding the basilica and its portico, after the fire of 1823;[151] two hundred in the excavations of S. Valentine's basilica, outside the Porta del Popolo. These last excavations are the only ones illustrating a Christian cemetery which are left visible; but their importance is limited. The cemeteries of Arles and Pola, alluded to by Dante, have disappeared; and so has the magnificent one of the officers and men employed in the Roman arsenal at Concordia Sagittaria, which was discovered in 1873, near Portogruaro, by Perulli and Bartolini. This cemetery, which contains, in the section already explored, nearly two hundred sarcophagi, cut in limestone, in the shape of Petrarch's coffin, at Arquà, or Antenor's at Padua, was wrecked by Attila in 452, and buried soon after by an inundation of the river Tagliamento, which spread masses of mud and sand over the district, and raised its level five feet. The accompanying plate is from a photograph taken at the time of the discovery.