How much have these numbers been trifled with! The seven arms of the chandelier in the temple of Jerusalem, the seven days of the week, and even the seven planets have been pressed into the service to explain them. But such explanations may be found for any number. At the time of the French revolution I knew a good-natured man, who enthusiastically took up every change and demonstrated that, as man has five fingers and five senses, the Directoire and the Council of the Five Hundred was the most perfect form of government. When there were three consuls, he comprehended this too and found it quite natural; and when at last there was only one, he declared that it was all right, for that unity must prevail in nature. Such trifling with numbers is a bad thing. I have already spoken to you about the physical character of the whole district. The ground is volcanic, the stones are tufo, and the loose soil puzzolano. These volcanic substances are very useful as cement and very durable. Wherever in architectural structures the ancients speak of _arena_, we have to understand puzzolano; we translate it indeed by “sand,” but it is a volcanic sand. Thus we read in Cicero’s speech for Cluentius that a dead body was found in a sand-pit (_arenaria_); such pits were dug very deep and were very extensive. Of the same kind are the catacombs at Rome: they are large subterraneous passages, which, if due care was taken in their construction, did not fall in. In my lectures on Roman antiquities, I have said that these catacombs were the ordinary burial places for the poor. This much may suffice about the hills.