properly GROTTA, a cave, natural or artificial, in the face of a rock or a mountain.

Among the more remarkable artificial works of this kind may be mentioned the famous Grotta di Paolillo, which is a straight passage cut through the rock from Naples to Pozzuoli, about 1000 paces in length, 80 or 90 feet high, from 24 to 30 feet wide, and forming the main road for the daily traffic of a very populous district. See PAOLILLO. But the most remarkable examples of artificial caverns in the world are to be found in the ancient Petra, which may be called a city of caves or grottoes. See PETRA.

Of natural grottoes, it will only be necessary here to name a few of the most remarkable in their several ways, in order to facilitate reference to those parts of the work where they are more particularly described. Among these are the celebrated caverns of Illyria, in the Julian Alps—moun-