(relevant entries linked from the text)
Overlooking the Chiaia section of town, the Egg Castle and what appears to be an small eruption of Mt. Vesuvius, but I suspect that the lithographers touched this one up. There was a powerful eruption in 1872 another one in 1906, and a few smaller ones between 1900 and 1903, but nothing nice and dainty like this one. Maybe the photographers got tired of waiting around. Here is an entry on "Recent Eruptions of Vesuvius."