The Alban Hills (Italian Colli Albani) are the site of a quiescent volcanic complex in Italy, located 20 km (12 mi) southeast of Rome and about 24 kilometres (15 mi) north of Anzio.  The dominant peak (but not the highest) is Monte Cavo at 950 m. There are two small calderas which contain lakes, Lago Albano and Lake Nemi. The rock of the hills is called Peperino (lapis albanus) a particular Tuff, a combination of ash and small rocks that is useful for construction, and provides a mineral-rich substrate for grape vines.  

 http://en.wikipedia.org/wiki/Alban_Hills