Balkan Peninsula, the most easterly of the three large peninsulas which form the southern extremities of the European continent. Its area, 184,779 sq. m., is about 35,000 sq. m. less than that of the Iberian Peninsula, but more than twice that of the Italian. Its northern boundary stretches from the Kilia mouth of the Danube to the Adriatic Sea near Fiume, and is generally regarded as marked by the courses of the rivers Danube, Save and Kulpa. On the E. it is bounded by the Black Sea, the Sea of Marmora, and the Aegean; on the S. by the Mediterranean; on the W. by the Ionian Sea and the Adriatic. With the exception of the Black Sea coast and the Albanian littoral, its shores are considerably indented and flanked by groups of islands. The Peninsula in its general contour resembles an inverted pyramid or triangle, terminating at its apex in a subsidiary peninsula, the Peloponnesus or Morea. Its surface is almost entirely mountainous, the only extensive plains being those formed by the valleys of the Danube and Maritza, and the basin of Thessaly drained by the Salambria (ancient Peneus). The Danubian plain, lying, for the most part, outside the Peninsula, is enclosed, on the north, by the Carpathians; and on the south by the Balkans, from which the Peninsula derives its name.

These ranges form together the great semicircular mountain-chain, known as the anti-Dacian system, through which the Danube finds a passage at the Iron Gates. The other mountain-systems display great complexity of formation; beginning with the Dinaric Alps and the parallel ranges of Bosnia, they run, as a rule, from north-west to south-east; the great chain of Rhodope traverses the centre of the Peninsula, throwing out spurs towards the Black Sea and the Aegean; farther west are the lofty Shar Dagh and the mountains of Montenegro and Albania, continued by the Pindus range and the heights of Acarnania and Aetolia. The principal summits are Olympus (9794 ft.), overlooking the Gulf of Salonica; Musallá (9631) and Popova Shapka (8855), both in the Rhodope system; Liubotrn in the Shar Dagh (8989); Elin, in the Perin Planina (8794); Belmeken in southern Bulgaria (chain of Dospat, 8562); Smolika in the Pindus range (8445); Dormitor in northern Montenegro (8294); Kaimakchalan in central Macedonia (8255); and Kiona in Aetolia (8235). Owing to the distribution of the mountain-chains, the principal rivers flow in an easterly or south-easterly direction; the Danube falls into the Black Sea, the Maritza, Mesta, Struma (Strymon), Vardar and Salambria into the Aegean. The only considerable rivers flowing into the Adriatic are the Narenta, Drin and Viossa. The principal lakes are those of Ochrida, Prespa, Scutari and Iannina. The climate is more severe than that of the sister peninsulas, and the temperature is liable to sudden changes.

The winter, though short, is often intensely cold, especially in the Danubian plain and in Thrace, the rigorous climate of which is frequently alluded to by the Latin poets. Bitter north-easterly winds prevail in the spring, and snow is not uncommon even in the low-lying districts of Greece. The autumn weather is generally fine and clear.