Another inscription, discovered in 1864, deserves attention on account of the instruments which are engraved upon it. It is a fragment from the tomb of a dentist named Victorinus, or Celerinus, with the representation of the instruments he used in extracting teeth. Such representations are by no means rare on gravestones. The other two specimens reproduced here are also from the catacombs. Alexander was a dentist; the unknown owner of the other slab was a general surgeon, yet the symbol of dentistry occupies the prominent place in his display of tools. In my experience of Roman or Latin excavations, in which thousands of tombs have been brought to light, I have hardly ever met with a skull the teeth of which showed symptoms of decay, or evidence of having been operated upon by a professional hand. Specimens of filling are even more rare than those of gold plating. Of this latter process we have now a beautiful sample in a skull discovered in the excavations of Faleria, and exhibited in the Faliscan Museum at the Villa Giulia, outside the Porta del Popolo. The gold socket or plating of three molar teeth is still in excellent condition. And here I may recall the ancient law, mentioned by Cicero (De Leg. ii. 24), which made it illegal to bury a body with gold, except such as had been used in fastening the teeth. THE CEMETERY AD DUAS LAUROS (of SS. Peter and Marcellinus).[170] To the left of the second milestone of the Via Labicana there was an imperial villa, named _ad Duas Lauros_ (the two laurels), where the empress Helena was buried by Constantine, and Valentinian III. was murdered when playing with other youths, in 455. Adjoining the tomb of the empress, which was described in chapter iv., pp. 197 sq., were two cemeteries,--one above ground, belonging to the "Equites Singulares," or body guards; the other, below. The latter was the largest of the Via Labicana, and was known in early Church annals under the same name as the imperial villa. In 1880-82 a third and deeper network of galleries was excavated for the sake of extracting the pozzolana, the beds of which support the tufa and the catacombs excavated in it. Some damage was done to the tombs, but the Italian proverb _Non tutto il male viene per nuocere_ proved true once more on this occasion. The excavation of the catacombs, which is generally a difficult and costly work, and sometimes impossible, when the owner of the ground above them objects to this form of trespassing on his estate, here became an easy matter, the earth being simply thrown into the sandpits from the catacombs above. The discoveries made on this occasion, added to the descriptions and drawings left by former explorers, give us a thorough knowledge of these labyrinths. The impression which they make at first is rather poor; but this is due chiefly to the ravages committed by early explorers.