Immediately to the west of Thrace, Macedonia (Makedonia) is the largest region of Greece, including thirteen prefectures and the Monastic Republic of Mt. Athos, an autonomous area. Like Thrace, Macedonia is the Greek portion of a geographically larger area that now is politically divided among three countries. Besides the Greek region, the term Macedonia has included southwestern Bulgaria and southern FYROM which, until 1991, was the southeasternmost constituent part of former Yugoslavia. Greek Macedonia extends westward from the Nestos River to the Albanian border. The southern border is the Aegean coastline, and the northern border is determined by the mountain ranges that extend from Bulgaria and former Yugoslavia. The most notable topographic feature is the Chalkidiki Peninsula, which extends three fingers of land southeastward into the Aegean Sea. Mt. Athos rises over 2,000 meters from the eastern peninsula and has provided seclusion for a legendary monastic community for more than a millennium.
The terrain of Macedonia is primarily rugged mountains interspersed with fertile river valleys and an extensive coastal plain defined by the Axios River, which empties into the Aegean Sea after flowing southward from the FYROM. The valleys of the Vardar and the Struma rivers, and the Plain of Drama in the far east, are Macedonia's agricultural centers. Greece's second-largest city and second-largest port, Thessaloniki (Salonika), is located between the Chalkidiki Peninsula and the mouth of the Vardar. West of Thessaloniki is a plain drained by the Axios and Aliakmon rivers; the latter arises in the Pindus Mountains near the Albanian border and meanders eastward to form a swampy delta shared with the mouth of the Vardar just to the east. The delta then empties into the Gulf of Thermaikos, the northwesternmost extension of the Aegean Sea. The largest Macedonian island is Thassos, northeast of the Chalkidiki Peninsula.
Thessaloniki is located on the natural harbor of the Gulf of Thermaikos. The harbor ranks Thessaloniki second in importance as a Greek port, after the Piraeus complex south of Athens. In the postwar industrialization process, Thessaloniki's harbor came to serve new manufacturing complexes in the interior, and the city regained the commercial importance it had during the Middle Ages. Beginning in the 1950s, the city was redesigned and modernized. The Thessaloniki International Trade Fair is an important commercial event in the eastern Mediterranean.
The city was founded in 315 BC; its Christian community was the recipient of the epistles of Saint Paul to the Thessalonians that form two books of the New Testament of the Bible. Because it contains numerous sites of Hellenistic and Byzantine church buildings, Thessaloniki has become a center for the study of ancient architecture. The city belonged to the Byzantine Empire in two different periods, between which it was sacked and occupied by several tribes and kingdoms. The Ottoman Turks took Thessaloniki in 1430. In the late 1400s, the city was an important refuge for Jews driven from Spain, and it remained the center of Greece's Jewish population until the Nazi occupation virtually extinguished it. In modern times, Thessaloniki was the initial headquarters of the Young Turk movement in 1908, before becoming part of the Greek kingdom in 1913. It was a World War I base of Allied operations against Turkey as well as the capital of the breakaway pro-Allied government of Eleftherios Venizelos.
The island of Thassos, in the Aegean Sea near the mouth of the Nestos River, has rich mineral deposits that supported a prosperous community. The island changed hands frequently in the first millennium B.C. Its minerals long ago exhausted, Thassos became a tourist resort in the 1970s. Offshore oil deposits have been exploited in the 1980s and early 1990s.