The Greek territory, mainly mountainous (over 40% is located at altitudes above 500 m), reached its current configuration only in a relatively recent geological age, at the end of the Cenozoic and the beginning of the Neozoic. In fact, in that epoch those conspicuous orogenetic and epyrogenic phenomena took place which caused the sinking below the sea level of a large part of the vast Paleozoic plate, now constituted by the Aegean bottom, the folding of the mountain alignments of the Dinaric system and the formation of uplifts. localized, intermontane subsidence basins and coastal depressions according to a complex and inarticulate system of fractures and faults. The result is a tectonically very tormented structure, which is expressed with great evidence in the fragmentation of the territory, that is, in the frequent alternation of reliefs and depressions, arranged according to almost always irregular and unexpected orientations, and in the extreme articulation of the coastal contour. From a lithological point of view, sedimentary formations prevail, especially limestone, dating back to the Mesozoic and upper Cenozoic, in the western and central mountainous region, while in the areas facing the Aegean, extensive schistose-crystalline formations of the Paleozoic emerge. Karst phenomena are frequent in the limestone areas, which contribute to giving the Greek landscape that rocky and parched aspect, poor in arable land.
According to itypeusa, the north-eastern sector of the country, bordered by the Mesta River and the border with Turkey (Marica River) and Bulgaria, corresponds to the western part of the historical region of Thrace and extends from the Rodópē to the Aegean, including the southernmost ridge of that mountain massif and its last buttresses with various peaks above 1000 m, as well as an alluvial plain bordered by a low and marshy coast. AW of Mesta and up to the border with Albania extends the southern sector of Macedonia, divided with Bulgaria and the Republic of Macedonia. It is a vast region made up of mountainous reliefs, intermontane basins and an alluvial plain, formed by the sedimentary contribution of the Aliákmōn and the Vardar, whose valley – which extends deeply into the territory of the Republic of Macedonia – has formed, and still represents, but much less than in the past, one of the main commercial and cultural lines between the East and the West. Between the plain crossed by the Vardar and the Struma valley rises the wide mountainous ridge of the Vertískos Óros, which extends from NW to SE as far as the Aegean at the Gulf of Orfánion. Among this deep inlet, where the mouth puts the Struma, and the western Gulf of Thessaloniki goes Aegean mountainous Chalkidiki ending in S with the three digits long peninsula of Cassandra, Sithonia and Mount Holy, separated by deep gulfs of Cassandra and Monte Santo. In the western section of Macedonia the reliefs are higher and correspond to large strips of an ancient penepian, in which the tectonic adjustment movements have operated deeply, giving rise to pronounced sinkholes.
Further to the W and SW the relief is formed by a fairly regular series of mountain ranges that extend parallel to the Ionian in the NW-SE direction for a width of approx. 120 km and consist mainly of limestone formations. The highest of these ranges is that of the Pindos (Smólikas, 2637 m), deeply engraved by long transversal valleys which make communication between Epirus and Thessaly easier. From the Pindus various mighty buttresses detach, directed to the NE, to the E and to the SE. Of the two largest that embrace the plain of Thessaly, the northernmost reaches 2917 m in Mount Olympus, the highest peak in all of the Greek territory. Proceeding towards the S, the relief again splits into an irregular succession of chains, isolated massifs, intermontane basins and small coastal plains. A very particular structure presents the Peloponnese, which constitutes the southern extremity of mainland Greece. It is a squat mountainous peninsula, clearly detached from the mainland by the gulfs of Patras, Corinth and Aeginaand connected only by the narrow isthmus of Corinth, cut by the canal of the same name in 1893. It represents the direct continuation of the limestone reliefs of the Pindus and branches to the S in four rocky peninsulas, separated by the gulfs of Messenia, of Laconia and of Nafplio. Insular Greece, which represents 19% of the Greek territory by extension, is made up mainly of the highest parts of a vast submerged Paleozoic plate. The main islands are the Ionian ones (Corfu, Lefkada or Santa Maura, Kefalonia, Zante, Ithaca and other minor ones) in the Ionian Sea; Euboea, the Cyclades, the Northern and Southern Sporades, partly Asiatic, in the Aegean; and finally Crete, the largest and most important, between the Aegean and the Mediterranean itself.