From H.V. Morton’s account of his trip to the catacombs in his classic travelogue A Traveller in Rome, which I review briefly for Amazon:

“One’s first feeling of dismay at finding oneself in this dusty maze of death is soon replaced by an affectionate fellow feeling for those who had lived so long before us and had trodden out the first paths of faith. They must have been much like ourselves. Who can see without emotion the words they wrote when they closed the eyes of those they loved, the words we still use: not the hopeless pagan ‘Vale,’ but ‘Vivas in Deo’ and ‘In pace Christi.'”