Greece , officially the Hellenic Republic, known also as Hellas, is a country located in Southeast Europe. Its population is approximately 10.7 million as of 2018; Athens, the nation's capital, is its largest city, followed by Thessaloniki. Situated on the southern tip of the Balkans, Greece is located at the crossroads of Europe, Asia, and Africa. It shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to the northeast. The Aegean Sea lies to the east of the mainland, the Ionian Sea to the west, the Cretan Sea and the Mediterranean Sea to the south. Greece has the longest coastline on the Mediterranean Basin and the 11th longest coastline in the world at 13,676 km in length, featuring many islands, of which 227 are inhabited. Eighty percent of Greece is mountainous, with Mount Olympus being the highest peak at 2,918 metres . The country consists of nine traditional geographic regions: Macedonia, Central Greece, the Peloponnese, Thessaly, Epirus, the Aegean Islands , Thrace, Crete, and the Ionian Islands. Greece is considered the cradle of Western civilization, being the birthplace of democracy, Western philosophy, Western literature, historiography, political science, major scientific and mathematical principles, Western drama and the Olympic Games. From the eighth century B.C., the Greeks were organised into various independent city-states, known as poleis , which spanned the Mediterranean and the Black Sea. Philip II of Macedon united most of present-day Greece in the fourth century B.C., with his son Alexander the Great rapidly conquering much of the ancient world, from the eastern Mediterranean to India. The subsequent Hellenistic period saw the height of Greek culture and influence in antiquity. Greece was annexed by Rome in the second century B.C., becoming an integral part of the Roman Empire and its successor, the Byzantine Empire, which adopted the Greek language and culture. The Greek Orthodox Church, which emerged in the first century A.D., helped shape modern Greek identity and transmitted Greek traditions to the wider Orthodox world. After falling under Ottoman dominion in the mid-15th century, Greece emerged as a modern nation state in 1830 following a war of independence. The country's rich historical legacy is reflected in part by its 18 UNESCO World Heritage Sites. Greece is a unitary parliamentary republic and developed country with an advanced high-income economy, a high quality of life, and a very high standard of living. Its economy is the largest in the Balkans, where it is an important regional investor. A founding member of the United Nations, Greece was the tenth member to join the European Communities and has been part of the Eurozone since 2001. It is also a member of numerous other international institutions, including the Council of Europe, the North Atlantic Treaty Organization , the Organisation for Economic Co-operation and Development , the World Trade Organization , the Organization for Security and Co-operation in Europe , and the Organisation internationale de la Francophonie . Greece's unique cultural heritage, large tourism industry, prominent shipping sector and geostrategic importance classify it as a middle power.