Great Wall of China A line of fortifications across northern China. Originally built during the Qin Dynasty (221-206 bc) by connecting earlier fortifications, it was subsequently rebuilt and altered many times. The wall reached its greatest extent during the improvements of the Ming Dynasty (1368-1644), when it was expanded to about 6,400 km (4,000 mi) long.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.Great Wall of China n (Placename) a defensive wall in N China, extending from W Gansu to the Gulf of Liaodong: constructed in the 3rd century bc as a defence against the Mongols; substantially rebuilt in the 15th century. Length: over 2400 km (1500 miles). Average height: 6 m (20 ft). Average width: 6 m (20 ft) Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Great? Wall? of Chi?na n. a system of fortified walls with a roadway along the top, constructed as a defense for China against the nomads of the regions that are now Mongolia and Manchuria: completed in the 3rd century B.C., but later repeatedly modified and rebuilt. 2000 mi. (3220 km) long. Also called Chinese Wall. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.