In the regions of Latium and Campania contained by the Apennines there is a heterogeneous zone of geology, dominated by volcanic activity and lower limestone relief. The most prominent (1,000-1,500 m) of this limestone relief, formed by the
Lepini, Aurunci, and Ausoni mountains, separates a northern (Latium) from a southern (Campanian) province of volcanic activity.
The northern volcanic province of Latium has generally an older history which started in Pliocene times, as in the case of the Tolfa mountains, and ceased activity in the Pleistocene. Some of the recent dates of this activity are in the order of 95,000 to
90,000 years ago, although some lake deposits dated to about 40,000 years ago have been overlain by the most recent volcanic material (Tufo Giallo di Sacrofano). 0 By the republican period, volcanic activity would have been long distant, and the distinctive byproducts of the landscape would have been more important. For instance, the Tolfa mountains were an important source of metal ores. The morphology of the landscape is dominated by truncated, flat cones of low height, but wide diameter (up to 30 km). To the north of the Tiber, some of the original calderas are occupied by deep lakes (e. g., Bolsena, 146 m deep, and Vico and Bracciano, 160 m deep). Two of these lakes, Bolsena (114.5 sq km) and Bracciano (67.5 sq km), are the second and fourth largest lakes of the peninsula. A further volcanic lake, Baccano, was drained in Roman times. Four of these lakes have produced pollen sequences which show clearance of vegetation from their often steep, internal slopes during the last 2,500 years, at least in part coinciding with the republican period.11 In particular, the Monterosi sequence has been tied into the construction of the Via Cassia and contemporary villa construction.
South Etruria (or more exactly southeast Etruria) provides an important and well-studied region both from an archaeological and a landscape perspective. Studies of the geology show how the stratigraphy of a volcanic landscape can support the procurement of a wide range of resources.12 The harder volcanic rocks provide selci for road surfaces which can be sourced to particular deposits. The softer tuffs provided ready building material, easily cut into blocks for house foundations. Travertines, which precipitated out on the flanks of the Apennines, provided an alternative source of building material (see also Chapter 16). The Plio-Pleistocene clays below these volcanic deposits, revealed by the downcutting of the river systems, offered ready access to material for pottery production. The early work on sources and supply of raw materials is now being taken much further. Different geological zones supplied different building materials.13 Leucitic balsalts from the Lake Bolsena region were suitable for millstones. On the east side of the Tiber volcanic materials predominated. On the west side of the Tiber, the limestone of the Apennine ranges provided the key local materials. Economic efficiency determined that heavy local materials were frequently employed for construction unless water transport was readily available.
Studies of erosion and sedimentation in this region have shown dramatic changes to the local environment.14 Initially these were interpreted as a product of climatic change.15 More recent studies have demonstrated quite clearly at least a contribution of human impact. More specifically, Roman activity contributed greatly to these human-induced changes. Roman rivers and floodplains were very different to those of today. They were distinguished by a regime of shallow, actively migrating channels which were depositing bars of gravel. These conditions may in turn have necessitated some of the Roman engineering schemes to control and traverse the changing environment.
To the south of the Tiber, the Alban hills comprise both secondary volcanoes within older calderas and smaller crater lakes (e. g., Albano, Nemi) formed by explosive events. The peak of volcanic activity in the Alban hills was between 700,000 and
350,000 years ago. Much of the intervening area is filled with plateaux formed by tuff generated by ignimbrite extrusions, ash, and mud flows. These have often been dissected by rivers, cutting down to underlying Pliocene clays.
The southern volcanic province of Campania has remained active into very recent times, most notoriously in ad 79. The morphology is broadly similar to that of the northern Latium province, but still in an earlier stage of evolution, given its continuing activity. For this reason, Vesuvius is today the highest peak, reaching some 1,277m, and has a better-defined cone shape. Other areas, such as the Phlegrean fields, retain a diversity of cones and craters and the plains north of Naples contain extensive plains of tuff. The properties of this region are more extensively discussed below.
World History
