The 7 Hills of Rome

 

Two well accessible publications address specifically the recent geological development of the surroundings of Rome, including the notorious Seven Hills.

  • Heiken, Funiciello & Di Rita 2007 – The seven hills of Rome, a Geological Tour of the Eternal City.

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In this popular-scientific book, the geology of Rome is discussed from detail (starting with Trevi fountain) to general, with a particular attention to the interaction of geology, history and society. In the annex, field trips in and around Rome are proposed. The chapters are arranged geographically and cover each of the seven hills, the Tiber floodplain, ancient creeks that dissected the plateau and ridges that rise above the right bank.

Rome’s geological setting provides a myriad of natural benefits: proximity to a major river with access to the sea, plateaus affording protection, nearby sources of building materials, and clean water from spring in the Apennines, which, at least in the last part, could be conducted to the city over a flat plain.

The seven hills are actually eroded remnants of a volcanic plateau dissected over many centuries by streams. The origin of these deposits are the Volcano of the Colli Albani to the SE and the Sabatini volcanic complex to the NW of the city.

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Rising of the sea level caused in the final Pleistocene and the Holocene the progressive infill by alluvial deposits of the  Tiber valley and its tributaries (the dashed frame shows the area of the next block diagram). Legend: 1. Alluvial deposits of the Tiber River and its tributaries  2. Products of the Sabatini volcanic District 3. Products of the Colli Albani Volcano 4. Monte Mario formation 5. Fosso della Crescenza formation 6. Monte Vaticano formation (modified from Parotto 2008).

WP_parotto_2

The surroundings of Rome about 10.000 years ago, prior to the major anthropical changes. The Tiber alluvial plain is bounded on one side by the Gianicolo – Mt. Mario hill, with sedimentary rocks, including Pliocene marine clay, and with a thin volcanic cover and, on the other side by the remnants of the margin of the Colli Albani volcanic deposits, dissected through fluvial erosion in separate reliefs, among which the famous Seven Hills (modified from Parotto 2008).


This publication offers a concise and up to date overview of the geological setting of Rome, the available water and building stones resources, and the history of its urban development.

In the following text only the part relative to the last geological periods is cited; for the bibliographical details we refer to the original article.

  • Pliocene.

The area corresponding to the future Campagna Romana was submerged by the Tyrrhenian sea and formed an articulated continental platform from which isolated blocks emerged to form islands (Monte Soratte and Monti Cornicolani). The marine open-marine shales were deposited during the Pliocene, presently form the hundreds of meters thick bedrock of the area with very low permeability and over-consolidated characteristics. These shales are named Monte Vaticano formation. At the transition Upper Pliocene – Lower Pleistocene, an episode of tectonic uplift occurred favouring a temporary emersion of structural highs, namely of the Monte Mario high, where the Monte Vaticano formation MVA is eroded at the top by a planar erosional surface.

  • Lower Pleistocene (Santernian-Aemilian).

After the episode of tectonic uplift and emersion, the Roman area was again submerged. The Pliocene Monte Vaticano formation is overlain, above a subhorizontal erosional unconformity, by Lower Pleistocene (Santernian) infralittoral sandstone and siltstone which form the Monte Mario formation (MTM). These rocks culminate along the NW-trending Monte Mario structural high and mostly crop out along the right bank of the Tiber river valley. The Monte Mario structural high was formed during a prolonged period of time. An early phase of uplift was responsible for the shifting toward the west of the centre of deposition, where, during the late Lower Pleistocene (Emilian) open marine clays, with Hyalinea Baltica, were sedimented (Monte delle Piche formation – MDP).

  • Lower (Sicilian/Villafranchian) – Middle Pleistocene p.p.

The marine domains extinguished progressively from east to west due to the regional uplift of the area. The complete transition from marine to continental environments occurred between the late Lower and the early Middle Pleistocene, approximately between 850 and 700 ka, when the Roman area hosted the deltaic sedimentation from a paleo-Tiber river (Ponte Galeria formation – PGL).
The last phase of uplift of the NW-trending Mt. Mario structural high isolated the deltaic sedimentary wedge and forced the paleo-Tiber toward the south-east, parallel to the coast, inside a NW-trending subsiding valley wherein a thick succession of fluvial conglomerates was deposited, named the Fosso della Crescenza formation. The fluvial conglomerates of the Fosso della Crescenza formation are found as deep as -100 m below sea level.

  • Middle p.p.-Upper Pleistocene (700-125 ka)

As a consequence of the Tiber river diversion parallel to the coast, a large lake or swamp probably developed in the Colli Albani area, bearing an influence upon the early phreatoplinian activity of the volcano which started at about 600 ka (Pisolitic Tuffs succession). The growth of the Colli Albani volcano to the south, and especially the early emplacement of the large volume ignimbrite sheets (600-355 ka), progressively shifted the river back northward (after ca. 550 ka), approximately where the present day river has its course, where it cross-cuts the Monte Mario-Gianicolo horst (likely captured by a minor valley cut on the west flank of the Monte Mario rise) to find its way to reach the sea.
Contemporaneously, the Sabatini volcanoes to the north emplaced large volume ignimbrites, pushing the course of the Tiber river eastward near the Apennines.

  • Last Glacial Age.

The volcanic activity at the Colli Albani and Sabatini volcanoes during this period was essentially phreatomagmatic forming several maars. The progressive reduction of the erupted volumes, with the consequence of reducing considerably the production of volcanic debris, allowed the climate changes to have a stronger influence on the landscape evolution. During the last low stand of the sea level related to the Wuermian glacial age, the Tiber river valley deeply eroded the volcanic and pre-volcanic rock succession down to the Pliocene clay units. The Campagna Romana assumed the present configuration with perched relics of the tabular volcanic plateau, which represent the present day topographic reliefs of Roma.

  • Holocene.

The rise of the sea to the present level has induced the progressive filling of the Tiber river valley with its alluvial deposits, forming the alluvial plain closed to the west by the Monte-Mario-Gianicolo ridge, and, to the east, by the relics of the margin of the volcanic plateau, the notorious Seven Hills of Roma.

  • Recent developments.

The large flat plain that extends northwestward from the Albano maar lake in direction of Roma, the Ciampino Plain has been formed by the deposition during the Holocene of phreatomagmatic and lahar deposits from the most recent activity of the Albano maar. The last episode of lake overflow occurred in the IV cent. BC and induced the Romans to excavate a tunnel to drain the lake, which still today regulates the lake level 70 m below the crater rim.
The Ciampino Plain has been used later as the path for all Roman aqueducts, changing forever the social perception of that area from the source of disastrous floods in the main water way to the city.


- Heiken G., Funiciello R., De Rita D., 2007. The seven hills of Rome, a Geological Tour of the Eternal City. Princeton University press, p. 1-245, ISBN: 0-691-06995-6.
- Parotto, M. 2008. Evoluzione paleogeografica dell’area romana: una breve sintesi. In Funiciello, R., Praturlon, A. & Giordano, G. (ed) La Geologia di Roma dal centro storico alla periferia. Memorie Descrittive della Carta Geologica d’Italia, LXXX, 25-39.
- Giordano G., Mazza R., 2010 – The Geology of Rome and Urban Areas: the legacy of Prof. Renato Funiciello. In: Journal of the VirtualExplorer, volume 36, paper 28, doi: 10.3809/jvirtex.2010.00277.