Analysis of information sources in references of the Wikipedia article "Μέγα Σινικό Τείχος" in Greek language version.
Beginning as separate sections of fortification around the 7th century B.C. and unified during the Qin Dynasty in the 3rd century B.C., this wall, built of earth and rubble with a facing of brick or stone, runs from east to west across China for over 4,000 miles.
