Two large systems of internal reliefs cross the Iranian plateau diagonally and converge to the south, where they merge with the marginal ranges. The first runs from Azerbaijan to Makran in the NW-SE direction .; often elevated over 3000 m., it reaches 4250 with the basaltic dome of Koh-i Hazar and 3419 with the Basman, volcano-solfatara located near its south-eastern end. The second runs from eastern Khorāsān to Belūcistān in the NNO.-SSE direction, forming the so-called watershed of Iran; although lower than the first, it rises to 4043 m. at its southern end the enormous volcanic mass of Koh-i Taftān. They are intensely bent chains, with granite and schistose-crystalline skeleton covered with Jurassic and Cretaceous limestones, masked on the periphery and in the depressions by predominantly Miocene Tertiary sediments; subject to strong atmospheric degradation in an arid climate, they often have the appearance of semi-buried ruins under accumulations of debris.
Between the marginal chains and the central ones, very extensive areas are depressed in the form of closed desert basins, which the rivers descending from the peripheral reliefs have partly filled with pebbly floods in the marginal regions and with thin deposits in the internal parts. Several types of basins are distinguished, corresponding to different stages of desert evolution: basins still having a perennial lake fed by large rivers (such as Lake Urmiyah and partly the Seistan), basins almost covered by clays and transformed into salty swamps (which is given the name of kevir), and reservoirs now entirely and permanently dried out (such as the Lūṭ).
The Urmiyah basin, at the extreme NO. of Iran, it is still sufficiently rich in water and has a high-altitude bottom (1250 m.); the lake occupies an area of 4500 sq. km., which in high waters extends up to 6000 sq. km. But the appearance of the other large basins, characteristic of Iran, is quite different. The greatest of all is Seistan, which is depressing to the east of the Iranian chain of watersheds; corresponds to a very large sag area over which it extends for 600 km. wide the desert. The river Hilmend is deeply embedded in it, which flows into the lake bed at an altitude of 512, divided by its enormous muddy, fertile and irrigated delta. A little less extensive is the Great Kevir (Dasht-i kevir), south of the western Khorāsān and Elburs ranges, an absolute desert in the center, less desolate at the edges. More at noon, between the two central chains sinks the Lūṭ, a vast clayey-saline desert, which reaches 300 m at its lowest point. and it is the most depressed and driest part of the plateau.
Finally, it can be added that the alluvial plains that adorn the outer slopes of the marginal ranges are also considered an integral part of Iran. Among them, the thin strip between the Elburs and the Caspian stands out for its climate and vegetation; only fertile where it can be irrigated is Afghan Turkestan, and so is Arabistān, at the foot of the Zagros, known for its oil fields.
Overall Iran, also for the conditions of the human population (see afghanistan ; belūcistan ; persia), can resemble an immense fortress whose vital ganglia are concentrated along the extended perimeter of its walls, where nature has not failed to open more or less easy passages to the outside. The prevailing importance of these marginal areas is underlined by their weight in the historical evolution of the region, by the peripheral position of the Iranian capitals (Tabrīz, Teherān, Herāt) and by the very fact that there has always been a lack of a single center that combines the trends of the different parts that make up the illusory unity. On the other hand, this position explains well why Iran was, like Anatolia,
Currently this falls within the ambit of three different states, two of which, at least nominally, independent (Persia, Afghanistan), one now reduced to a province of the Indian empire under direct English control (Belūcistān). But both the creation and the maintenance of these units find their raison d’etre more in the contrast of the great European powers that come into conflict (England, Russia), than in the spontaneous evolution of organisms capable of affirming a solid and lasting hegemony.. In one as in the other of the two independent states, political power remains more or less limited, moreover, by the effective power of the individual groups that compose it, precisely because each corresponds to different forms of economy.
For the medieval phase, in addition to the aforementioned works by the German, the following works should be kept in mind: E. Herzfeld, Paikuli, Monument and Inctription of the early history of the Sasanian Empire, Berlin 1924, which, in addition to almost all texts epigraphs from the Arsacid and Sassanid ages, it provides useful lexical information; C. Salemann, Mittelpersisch, in Grundriss der iranischen Philologie, cit., P. 249 ff.; R. Gauthiot, Essai de grammaire sogdienne, I: Phonetique, Paris 1914-1923, completed by E. Benveniste, Essai de gramm. sogd. , II: Morphologie, Syntaxe et Glossaire, Paris 1929; H. Reichelt, Das ” Nordarische “, in Indogerm. Jahrbuch, I (1913), p. 20 ff. See also: persia; saci; sogdiana.
Of the modern dialects W. Geiger gave an admirable exposition for his times, in Grundriss der iranischen Philologie, cit., I, ii, p. 201 ff. – Later publications on individual dialects are listed by H. Reichelt, in Gesch. der indogerm. Sprachwissenschaft, cit., P. 20 ff. An extensive historical discussion of modern Persian is found in Horn, Neupers. Schriftsprache, in Grundriss der. Iran. Phil. , cit., I, 21, p. 1 ff. Always useful are H. Hübschmann’s Persische Studien (Strasbourg 1895).