Starting from the principle that the geographical concept of border, even in the case of a political territory, must correspond to that of a natural obstacle, suitable for forming an area of isolation and therefore of protection all around the territory in question, we can say that this concept translates into a concrete reality for Italy, perhaps better than for any other European region. As is known, in fact, the Italian region is surrounded on three sides by the sea – hence its very marked peninsular character -, and on the side along which it joins the rest of the European continent it is surrounded by the Alpine chains, which, containing in their part median, for almost the entire arc, very high areas, covered with perennial snow or in any case uninhabited and inaccessible, together they constitute an excellent zone of isolation and protection. Therefore the individuality of Italy, clearly delimited between the three seas and the arc of the Alps, is a very ancient concept, which is already clearly expressed by Latin writers and which is then perpetuated with constant uninterrupted tradition up to our days, not only among geographers, but among writers and thinkers of every category and who had, by famous authors, magnificent definitions in prose and verse. Indeed, the individuality of Italy within the circle of the Alps and its seas is by no means a purely geographical concept, but a universally perceived and almost innate truth in the expression itself. Italy , according to the most common and concrete use of it. And it is also very ancient the concept that, if we want to determine a boundary line within that isolation zone which is constituted by the highest areas of the Alps, this is to be made to coincide with the main watershed. This concept, which can be read clearly formulated by Latin writers, alluding to the divortia aquarum as well as to the Alpine limits of Italy, then finds from the century onwards. XVI its concrete expression in the geographical maps, not only Italian (see Magini’s map on p. 698), but also foreign ones. And even among writers (not only geographers, but also politicians) this tradition has persisted uninterrupted from the century. XVI onwards.
According to GLOBALSCIENCELLC.COM, the path of what is usually called the natural alpine border of Italy, is very evident almost everywhere, except in the extreme east, where, not only the alpine chains are lowered, and consequently, no longer continuous but occasional they meet. the very high, inaccessible and uninhabited areas responding to the more precise concept of border, but, due to the character of the territory, a karst type, with mainly underground hydrography, it is not even possible to always recognize a superficial watershed.
However, on the whole, the natural boundary line can be very clearly indicated, by unanimous designation of the geographers: a ) to the West by a branch of the Maritime Alps, which, departing from Mount Pelat, limits the Varo basin to the West, then from the line that, running along the crest of the Western Alps, divides the waters that go to the Po from those that go to the Rhone, from Mount Pelat to Mount Bianco; b ) to N. from the same current watershed line on the main crest of the Pennine and Lepontine Alps up to S. Gottardo, then from the watershed between the Po and the current Rhine on the high ridges of the Lepontine up to the Spluga, and from that between the Po and the Danube from Spluga to the Resia Pass, and between the Adige and the Danube from Resia to the Vetta d’Italia and the Sella di Dobbiaco; c) to the NE. and to E. still from the line of the watershed between the Danube and the Venetian rivers, marked by the main ridge of the Carnic Alps, then by the Julian Alps up to the pass known as Nauporto. TO SE. of this you enter the karst region mentioned above, in which the border can however be followed on the ridge that limits the basin of Lake Circonio to E. and contains the Cervaro, Nevoso, Jelenck and Rišnjak mountains, then descends with M. Tuhovič on the Canale del Maltempo to E. of the Buccari valley.
As for the maritime border, it should be noted first of all that the belonging to Italy of the three major islands is also a principle generally accepted since ancient times. Therefore to the W the boundary is evidently marked by the steep escarpment with which the short continental shelf flanking the Riviera di Ponente descends towards the maximum depths of the Ligurian Sea and by the very steep escarpment with which the wider platform, on which Corsica rests and Sardinia, descends towards the deep areas of the Hesperian Sea; there at 80 km. from the Sardinian coast it is already possible to reach depths of over 3000 m. To S. Pantelleria and the group of Malta undoubtedly belong to the Italian region, because they lie on the edge of the continental shelf constituting the base of Sicily, and Linosa, of volcanic origin, also falls within, for this character, among the volcanic island formations that surround Italy; instead Lampedusa would rather be ascribed to Africa, because it lies, beyond the Tunis Canal, on the African continental shelf and also has a tabular structure that brings it closer to northern Africa. In the Ionian and southern Adriatic, devoid of islands, the maritime boundary is very clear; much less in the northern Adriatic; however, there are undoubtedly attributable to the Italian region the Tremiti and Pelagosa and in the Quarnaro Cherso, Lussin and Veglia which are, under the aspect of the structure, a continuation of Istria (see the individual entries).
Within the natural boundaries mentioned above, Italy has an area of approximately 321,700 sq km.