196 



PHYSIOGRAPHY. 



[chap. 



sides of the crater, and it was in the natural fortress formed 

 by this great amphitheatre that Spartacus the Thracian, with 

 his Httle band of gladiators, took up his position at the 

 beginning of the Servile War in the year 72 b.c. Earth- 

 quakes, as already pointed out, are often the heralds of 

 volcanic eruptions ; and the first notice which the old 

 dwellers around Vesuvius received of its renewed activity 

 was from a series of earthquakes which began, as far as we 

 know, in a.d. 63, and continued intermittently for about 



■Flu. 55. — Summit of Vesuvius in 1767. 



sixteen years. These disturbances culminated in the great 

 eruption of a.d. 79, which has been described in two letters 

 written by Pliny the Younger to Tacitus. The elder Pliny, 

 the author of the famous Hisioria Naturalis, was, at that 

 time, in command of the Roman fleet off Misenum. On the 

 24th of August a cloud of unusual size and shape was seen 

 hanging over the mountain. It is described as having had 

 the form of a huge pine-tree ; and similarly- shaped masses 

 of cloud usually accompany the eruptions of Vesuvius. An 



