«Great Wall of China». A: Encyclopædia Britannica. «Large parts of the fortification system date from the 7th through the 4th century BC. In the 3rd century BC Shihuangdi (Qin Shi Huang), the first emperor of a united China (under the Qin dynasty), connected a number of existing defensive walls into a single system. Traditionally, the eastern terminus of the wall was considered to be Shanhai Pass (Shanhaiguan) on the coast of the Bohai (Gulf of Zhili), and the wall's length—without its branches and other secondary sections—was thought to extend for some 6,690 km (4,160 mi).»
João de Barros, Ásia de João de Barros. Dos feitos que os portugueses fizeram no descobrimento dos mares e terras do Oriente., 3-a Década. llibre 2, capítol VII. Lisboa, 1563. Aquest capítol està reproduït a les pp. 186—204 del cinquè volum de l'1777 edició d'Asia.
