Vesuvius is a humpbacked peak, consisting of a large cone (Gran Cono) partially encircled by the steep rim of a summit caldera caused by the collapse of an earlier (and originally much higher) structure called Mount Somma. The Gran Cono was produced during the A.D. 79 eruption. For this reason, the volcano is also called Somma-Vesuvius or Somma-Vesuvio.