The reign of Titus, though so short, was signalized by two great disasters. The first was a conflagration at Rome, which was almost as calamitous as the Great Fire in the reign of Nero. The second was the destruction, by an eruption of Vesuvius, of the Campanian cities of Pompeii and Herculaneum. The cities were buried beneath showers of cinders, ashes, and streams of volcanic mud. Pliny the elder, the great naturalist, venturing too near the mountain to investigate the phenomenon, lost his life. [Footnote: In the year 1713, sixteen centuries after the destruction of the cities, the ruins were discovered by some persons engaged in digging a well, and since then extensive excavations have been made, which have uncovered a large part of Pompeii, and revealed to us the streets, homes, theatres, baths, shops, temples, and various monuments of the ancient city--all of which presents to us a very vivid picture of Roman life during the imperial period, eighteen hundred years ago.] DOMITIAN--LAST OF THE TWELVE CÆSARS (A.D. 81-96).--Domitian, the brother of Titus, was the last of the line of emperors known as "the Twelve Cæsars." The title, however, was assumed by, and is applied to, all succeeding emperors; the sole reason that the first twelve princes are grouped together is because the Roman biographer Suetonius completed the lives of that number only. Domitian's reign was an exact contrast to that of his brother Titus. It was one succession of extravagances, tyrannies, confiscations, and murders. Under this emperor took place what is known in Church history as "the second persecution of the Christians." This class, as well as the Jews, were the special objects of Domitian's hatred, because they refused to worship the statues of himself which he had set up (see p. 322). The last of the Twelve Cæsars perished in his own palace, and by the hands of members of his own household. The Senate ordered his infamous name to be erased from the public monuments, and to be blotted from the records of the Roman state. THE FIVE GOOD EMPERORS: REIGN OF NERVA (A.D. 96-98).--The five emperors-- Nerva, Trajan, Hadrian, and the two Antonines--that succeeded Domitian were elected by the Senate, which during this period assumed something of its former weight and influence in the affairs of the empire. The wise and beneficent administration of the government by these rulers secured for them the enviable distinction of being called "the five good emperors." Nerva died after a short reign of sixteen months, and the sceptre passed into the stronger hands of the able commander Trajan, whom Nerva had previously made his associate in the government. [Illustration: TRAJAN.]