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San Leo: Territory


San Leo rises on a rhomboidal limestone and sandstone rock of about 480.000 square metres. The highest point is the southeastern portion of the rock, which then progressively lowers on the western side.


The castle, rises 639 meters above sea level and towers the valley from the top of the rocky peak with the overhanging rock faces that made it impregnable.
San Leo represents one of the most unique examples of what geologists call the offscraped Ligurian sequence of the Val Marecchia area. The definition itself gives us an idea of its complex geological structure: the “limits” of the sequence, or better, the plate, are the overhanging rock faces and we can easily see where the plate meets the underlying clay base, since there are no layer debris. This very specific structure makes San Leo a case in point for experts on the area’s geology, reflecting the geomorphological history of the whole region.
San Leo’s city centre rises on the outer portion of this very specific stone “blanket” or flow, famous among Italian and international geologists for its long and difficult history. The blanket, as they call it, is made up of several rocky formations which, over the centuries, layered on top of each other in a different area and later flowed to this very specific spot. It seems that the stone formations typical of Liguria, especially the Varicoloured clay shales are at the origins of the process. The entire Ligurian tethys formation might have flowed to the Montefeltro area more or less when the Apennines foredeep itselfs began.  During the flowing, new formations called Ligurian or neogenic were created and continued to follow the movements of the blanket. These formations, generally more resistant than the older ones, settled permanently in the area originating a phenomenon the experts refer to as neogenic formation or, more recently, Ligurian tethys. Many hypotheses have been proposed to explain the way these formations moved and settled here and a good deal of them are still unconfirmed.
In its lower section, San Leo’s rocky plate is made up of limestone, typical of the area of San Marino, whereas is upper part it is similar to the formations we usually find on a nearby mountain called Monte Fumaiolo. The difference between the two can easily be observed form the only access road to the town, on the right, just before the city gate. Varicoloured clay shales are easily recognized below the plate, on the eastern portion of the rocky cliff and in the gullies and rocks at the foot of it. Varicoloured clay shales are easily eroded by atmospheric agents, due to their poor geotechnical properties: rainwater leaks in progressively deforming the shales and triggering phenomena such as flows and sliding. These, together with deep fractures in the rock itself, sometimes cut down the very base of the plate leading to serious ground instability and slides. A very famous slide is the one occurred in the XVII Century, when the eastern gate collapsed, permanently changing the outlook of the town.

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  • How to reach San Leo, in Italy Getting here

    San Leo lies in Rimini's hinterland, in southern Emilia Romagna, on the border of Tuscany, Le Marche Region and the Republic of San Marino.
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