6 THE ROMAN COMAGMATIC REGION. 
Ciminian districts. It resembles the district first described, inasmuch as a sheet of 
water, Lake Bracciano, forms the topographic center. This lake, with an area of 
57.5 kilometers and a depth of 160 meters, has its surface 164 meters above sea- 
level. It is approximately circular in shape, with two or three small bays, and 
is surrounded on the west and north by a girdle of hills, which attain their highest 
altitude above sea-level (602 meters) at Monte di Rocca Romana on the north. Im- 
mediately to the east is the small Lago di Martignano, and the basins of two others 
are represented in the Stracciacappa Marsh and the Valle di Baccano, all three 
being distinctly elliptical or circular and surrounded by rings of hills or curving 
ridges. From the inner wall surrounding Lake Bracciano the land slopes down to 
the west, north and east rather regularly, though it is broken on the west by the 
Tertiary volcanic masses of Monte Calvario and Monte San Vito. On the south the 
hills along the lake shore are lower, and the slope southward is very gentle. 
The general topographic resemblance to the Vulsinian District is very marked, 
though the features are on a somewhat smaller scale. Moderni, who has studied 
this district very carefully, argues for it a structure analogous to that which he 
assigns to the Vulsinian. He regards Lake Bracciano as being, not a crater lake, 
but as a lake basin formed by the ejections of the surrounding volcanic vents, of 
which he enumerates and describes eight main ones, with their parasitic cones. This 
view is combated by Sabatini, so that, for the present, the question of the structure 
of the complex and the origin of the lake must be regarded as unsettled. 
Of the towns in the district the most important is Bracciano, on the crest of 
the western lake-rim. Smaller ones are Manziana and Oriolo on the northwest, 
Trevignano on the northern shore, near a small semicircular bay, and Anguillara 
on the southeast shore near the outlet of the lake. 
Latian District. 
The Alban Hills, which make up this district, are situated to the southeast of 
Rome, as is well known, and some 50 kilometers southeast of Lake Bracciano. The 
area covered by the volcanic complex is about 580 square kilometers. 
The complex consists of a circle of hills and summits, varying in altitude from 
550 to 939 meters, and with a diameter of about 15 kilometers. Up to this the sur- 
face rises gently from the north, east, and south, while on the west and southwest 
the regularity of this somma is broken by the lakes Albano and Nemi and the Valle 
Ariccia, the sites of late flanking eruptions. Inside the large circle there rises a 
fairly well-defined cone, attaining a height of 956 meters and with the crater known 
as Campo d'Annibale at the top. Monte Cavo forms the most prominent and 
almost the highest point of the rim encircling this. 
The structure is explained by Sabatini, who has made a careful study of the 
complex, as analogous to that of Somma and Vesuvius. The larger circle of hills 
is the crater of the earliest volcano, within which, at a later date, was thrown up the 
interior cone of Monte Cavo. The small lakes occupying the western slope, and 
