This is, perhaps, the most valuable part of the volume, for it contains more of the author’s own observations than the rest of the work. It deals more particularly with the great earthquake of 5th February A.D. 63, which occurred in his own country, and about which he could collect information at first hand. As already mentioned, the subject of earthquakes had long fascinated him, and he had published, in his youth, a volume about it. The calamity which brought so much injury to the towns of Campania was more especially likely to enlist his vivid interest, for the region that had been convulsed was with him a well-known and favourite part of Italy, where he often came to spend, on the shores of the Bay of Naples, such leisure as the life in Rome allowed him. Besides, it was the native district of Lucilius, to whom the volume was addressed, and whose town of Pompeii had suffered from the shock.[118] Hence he here plunges at once into details of the damage caused by this particular earthquake. As a prelude to his inquiry into the whole question of the origin of such catastrophes, he indulges in reflections on their appalling nature. Some of the unfortunate residents in the convulsed district had fled from it, vowing never to return. But where, the writer asks, can they be sure of safety, seeing that no quarter of the world is exempt from this form of danger? He urges that it is at least some consolation to be assured that such calamities are not the work of angry gods, as was popularly believed, but are traceable to their own special causes in the processes of nature (228). [118] In Seneca’s letters, frequent reference is made to his visits to the district. He seems generally to have taken a villa at Baiae, or some adjacent place on that western part of the coast. He appears to have been a poor sailor, glad to make for the nearest landing-place between Baiae and Naples, so as to escape from the pangs of sea-sickness. On one of his excursions he revisited Pompeii, and was set into a reverie of his youth there. See his _Letters_, 49, 51, 53, 55, 57, 70, 77. He then considers the various opinions entertained on this subject by earlier writers, which, on the whole, he regards as crude and inexact. The cause of earthquakes had been found in water, fire, air, and the earth itself, or in a combination of several of these agencies, or even in the co-operation of the whole of them. As regards the action of water, he dismisses the opinion of Thales (231), but in the statements of other authors, who maintain the power of internal water in causing earthquakes, he sees a greater probability of truth. He fully admits the existence of large rivers and extensive lakes inside the earth, and that in these dark uninhabited regions flooded rivers undermining their banks, and a swollen sea lashed into fury by the subterranean winds, may communicate shocks to the surface of the earth (234).