The legend, or key, is used to display what stuff means on the map. This makes it easier to spot, rivers, capitols, parks, hospitals and everything else that the map might be centralized upon. Its basically your guide to reading the map and its markings. <span />
Answer ( I don’t know if this is the answer your looking for but oh well...) The city of Pompeii is famous because it was destroyed in 79 CE when a nearby volcano, Mount Vesuvius, erupted, covering it in at least 19 feet (6 metres) of ash and other volcanic debris. The city's quick burial preserved it for centuries before its ruins were discovered in the late 16th century.
Castles were often built at crossroads to guard important or strategic sites.