The Monti della Tolfa are a series of hills of volcanic origin which form part of the Lazio Anti-Apennines, bordered to the west and south by the Tyrrhenian coast between Civitavecchia and Santa Severa, to the east by the Sabatini Mountains and to the north by Mignone river and the Cimini Mountains.
The rivers that cross the territory, and which flow into the Tyrrhenian Sea, are, following the coast from north to south:
•River Mignone
•Fosso del Marangone
•Castelsecco ditch
•Rio Fiume
Of these, the most important are Mignone and Rio Fiume. The Mignone originates in the Sabatini mountains, and crosses the territory of the Tolfa Mountains from East to West, marking their northern border. The Rio Fiume originates from the confluence of numerous streams that spring in the area between Monte Tolface and Monte Acqua Tosta.
Geology
The Tolfa mountains are made up mainly of trachytes formed as a result of the intense acid volcanic activity that affected the area of Tolfa, Cerveteri and Manziana between the Eocene and the beginning of the Pleistocene. These activities have originated in the territory three sectors with very different morphological characteristics:
The first sector, located between Tolfa and Allumiere, has a more marked orography (volcanites in domes and ignimbritic deposits) with elevations that can exceed 600 m (Monte delle Grazie and Monte Sassicari).
The second sector is the one between Tolfa and Civitavecchia, with the Tolface group, and is made up of isolated lava structures which form very steep walls.
The third sector is characterized by a large hilly area, which surrounds the entire mountain system and has gentle slopes which descend gradually towards the valley crossed by the Mignone.
Minerals
Starting from the Pleistocene, the sedimentary and igneous rocks of the Monti della Tolfa area were affected by transformation phenomena which led to the formation of various types of minerals< /strong>. These phenomena are the result of a considerable circulation of fluids in the sedimentary basement and of the presence of high thermal variations caused by the existence of deep magmatic masses > which acted as an “engine” for the circulation of fluids.
The final results of these mineralization processes lead to different (mineral) results depending on the nature of the rocks involved and the chemical-physical conditions of the environment in which these processes took place. These processes have therefore formed in the territory rich deposits of kaolin and other minerals such as: blende, galena, pyrite, alunite and cinnabar. Another mineral present in the area is wavellite, very rare in Italy and whose presence, now definitively confirmed in the Allumiere area, is of great importance from a scientific point of view .
Alunite a alum
Particularly relevant are the alunite deposits, from which alum is extracted. Alum is a salt which in the past was of considerable importance for various processes, including those of the textile industries in which it was used as a color fixer and in the >wool processing, of the paper industries, in the processing of skins and in medicine for its hemostatic abilities.
The discovery of deposits of this mineral took place around 1460, by an official of the Papal State, Giovanni da Castro, who, observing the presence in the area of holly plants, already found in Turkey, which was then the main production site of substance, he had the intuition that there could be alunite in the ground. The initial discovery took place near the current hamlet of Allumiere, La Bianca.
The industrial exploitation of the deposits began in 1462 and continued for over three centuries following the technique of open-air excavation, and thus heavily altering the physiognomy of the landscape which even today reveals the cracks and craters used for the extraction of the material.
After 1500 the production of alum entered a phase of intense exploitation; the production plants were moved to the foot of Monte delle Grazie, a mineral processing plant was built complete with an aqueduct and a village for the workers. The complex was called Le allumiere and will become subsequently the current town of Allumiere.
In the following two hundred years the quarries of Monti della Tolfa became the most important in Europe, many new quarries were opened in various localities of the territory: in the Castagneto area, along the road leading to Le Cave, we have the sites of the Cava Grande , the Gregoriana, the Cavetta and the Clementine quarry. On the slopes of the Castagneto mountains, which will later turn out to be the area with the richest deposits of alunite, there are the Castellina quarry, the Cava dei Romani and the Rotella quarry.
In 1725 extraction was started from a new quarry, now known as Cavaccia, which will turn out to be the largest quarry. The excavations profoundly altered the territory, creating a sort of canyon in the mountain with vertical walls over 50 meters high. Today the place is no longer as it appeared then, as in recent years there have been land reclamation interventions that have partially filled the gully.
In the following years, the fortunes of the quarries worsened for two reasons: first, the discovery of important deposits in Spain made the Allumiere quarries lose their European monopoly, then in 1788, with the discovery of artificial alum, the quarries fell into a deep crisis .
In 1815, to recover competitiveness by lowering costs, a new excavation method was adopted: tunnel excavation. This system had significant advantages: better exploitation of the veins due to less waste material and continuous extraction no longer conditioned by meteorological events.
Between 1850 and 1870 various wells were dug throughout the territory. The most important are: Pozzo Gustavo (near Monte Urbano), the Cesarina gallery (in the direction of Cavaccia), the mines of Santa Barbara, that of Val Perella and those in the direction of Cava Grande. In 1868 three new deposits were discovered on the western slope of Le Cave: they are the Provvidenza, Trinità and Nord sites.
In 1870 the territory passed from the Papal State to the Italian State. The production plant was transferred to Civitavecchia, but by now production had considerably decreased due to the lower market demand for rock alum. Subsequently the factory and the extraction sites passed to the Montecatini Company, but by now the demand had decreased so much that the extraction was highly uneconomical, therefore in 1941 the company closed the plants and ceased the production of alum, which had lasted almost 500 years.
Archaeological sites
There are several archaeological sites in the area:
•Mount Elceto, where evidence of a Bronze Age settlement has been found;
•Monte Rovello, where excavations have brought to light various findings, the oldest of which can be dated back to the Middle Bronze Age;
•Tolaccia, where two different settlements have been identified, dating back to the Final Bronze Age, and some tombs referable to the Final Bronze Age and the Iron Age;
•Tufarelle, where the remains of a village dating back to the Neolithic were found.
Protection
The Tolfa Mountains are located in the Special Protection Area (SPA) of the Tolfetano-Cerite-Manziate district (IT6030005) which occupies an area of about 70,000 m in the territories of the municipalities of Allumiere, Barbarano Romano, Blera , Bracciano, Canale Monterano, Cerveteri, Civitavecchia, Manziana, Monte Romano, Oriolo Romano, Santa Marinella, Tarquinia, Tolfa, Vejano and Vetralla.