Silk Road (s?lk) An ancient trade route between China and the Mediterranean Sea extending some 6,400 km (4,000 mi) and linking China with the Roman Empire. Marco Polo followed the route on his journey to Cathay.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.