Well, yes, but actually no, but also yes? You may be interested in the following older answers:

• An old Monday Mysteries feature (boy is this way before my time) by /u/_dk;
• How effective was the Great Wall of China after its completion? answered by /u/bigbluepanda;
• Did the Great Wall of china really work? answered by myself; and
• Starting with the Qin Emperor in 222 BCE, China has a long history of building walls along the northern border to keep out the "barbarians". This, of course, culminated with Great Wall under the Ming. How effective were these walls? Did they ever successfully prevent an invasion from the north? answered by /u/cthulhushrugged