We need not, however, go back five centuries for facts that bid men heed what may be passing underground about the shores of this blue bay. Here is one too large to be overlooked, immediately in front of us--no other than the green slope of Monte Nuovo, a hill of aspect both innocent and ancient, ridged with a few pine trees by whose aid the mountain contrives to look as if it had stood there beside the Lucrine Lake as long as any eminence in sight. This is a false pretension. There was no such mountain when Petrarch climbed the neighbouring height, nor for full two centuries afterwards. What Petrarch saw exists no longer. He looked down upon the Lucrine Lake connected with the sea by a deep channel, and formed with Lake Avernus into one wide inlet fit for shipping. This was the Portus Julius, a harbour so large that the whole Roman fleet could manoeuvre in it. The canals and piers were in existence less than four centuries ago; and this great work, so remarkable a witness to the sea power of the Romans, would doubtless have lasted unto our day had it not been for the intrusion of Monte Nuovo, which destroyed the channels and reduced the Lucrine Lake to the dimensions of a sedgy duck pond. The catastrophe is worth describing, for no other in historic times has so greatly changed the aspect of this coast or robbed it of so large a portion of its beauty. For full two years there had been constant earthquakes throughout Campania. Some imprisoned force was heaving and struggling to release itself, and all men began to fear a great convulsion. On the 27th of September, 1538, the earth tremors seemed to concentrate themselves around the town of Pozzuoli. More than twenty shocks struck the town in rapid succession. By noon upon the 28th the sea was retreating visibly from the pleasant shore beside the Lucrine Lake, where stood the ruined villa of the Empress Agrippina, and a more modern villa of the Anjou kings, who were used, like all their predecessors in Campania, to take their ease in summer among the luxuriant vegetation of the hills whose volcanic forces were believed to be lulled in a perpetual sleep.