This is a news article in 1931, from Mordern Mechanix blog:
The Great Wall of China, long considered one of the most remarkable engineering feats in the world, may soon become one of the greatest and most unusual motor highways on earth if the plans of the Nationalist government are carried through.
The great wall was built about 220 B. C. by the first emperor of the Tsin Dynasty as a protection against the roving bands of Tartars, which were then in the habit of descending from the Mongolian plains and making sporadic raids upon the Chinese cities to the south. After 2150 years the wall is still in a remarkable state of preservation considering that only twice, in the fifteenth and again in the sixteenth century, were any extensive repairs made upon the structure.
The height of the wall ranges from twenty to forty feet, while at intervals of about two hundred yards are towers about 25 feet higher than the wall. The northern parapet of the entire fortification is loop-holed to protect the defenders from the missiles of the enemy, while the towers are surmounted by such a parapet around all four sides. Many of the towers are roofed over, and were no doubt used as barracks by the Chinese soldiers, while sentries were posted at the other towers.