Egypt, officially the Arab Republic of Egypt, is a transcontinental country that spans the Sinai Peninsula, which connects the northeastern corner of Africa to the southwest corner of Asia. Egypt is a Mediterranean country bordered to the northeast by the Gaza Strip and Israel, to the east by the Gulf of Aqaba and the Red Sea, to the south by Sudan, and to the west by Libya. Jordan is across the Gulf of Aqaba, Saudi Arabia is across the Red Sea, and Greece, Turkey, and Cyprus are across the Mediterranean, but none of them share a land border with Egypt. Egypt has one of the longest histories of any nation, dating back to the 6th–4th millennia BCE along the Nile Delta. Ancient Egypt is regarded as the birthplace of civilization, having witnessed the emergence of literature, agriculture, urbanisation, organized religion, and central government. The ruins of Memphis, Thebes, Karnak, and the Valley of the Kings, as well as the Giza Necropolis and its Great Sphinx, represent this legacy and remain a significant subject of science and popular interest. Egypt's long and rich cultural heritage is an important part of its national identity, reflecting the country's unusual transcontinental position, which encompasses the Mediterranean, Middle East, and North African regions. Egypt was an early and important Christian center, but it was largely Islamized in the seventh century and is now mostly Muslim, though with a substantial Christian minority. Egypt became a monarchy in 1922, when it declared independence from the British Empire. Egypt proclaimed itself a republic after the 1952 revolution, and in 1958 it joined with Syria to create the United Arab Republic, which lasted until 1961. Egypt experienced social and religious unrest as well as political turmoil in the second half of the twentieth century, fighting numerous armed conflicts with Israel in 1948, 1956, 1967, and 1973, and occupying the Gaza Strip intermittently until 1967. Egypt signed the Camp David Accords in 1978, formally withdrawing from Gaza and acknowledging Israel. Political instability, including the recent 2011 revolution and its aftermath, as well as terrorism and economic underdevelopment, continue to plague the region. Egypt's new government, a semi-presidential republic, has been labeled authoritarian or leading an authoritarian regime by a number of human rights watchdogs, who blame it for the country's poor human rights record. Egypt's official religion is Islam, and its official language is Arabic. Egypt is the most populated country in North Africa, the Middle East, and the Arab world, with over 100 million people, the third most populous in Africa, and the thirteenth most populous in the world. The vast majority of its inhabitants live along the Nile River's banks, which cover an area of about 40,000 square kilometers and contain the only arable land in the country.