There's a great debate about the efficiency of the Great Wall of China.
There are many pros and cons that both sides might argue about if it was or wasn't worth it to build the great wall.
Cons.
1. Millions of people died to build the Great Wall.
2. The main reason the have the Wall built was to keep invaders (Mostly Mongols) out of China, but eventually, they found their way around the wall anyways.
3. Considering that it cost time, resources and lives, many consider that the Wall of China was a mistake and a waste.
on the other hand, here are some of the arguments pro the Wall.
1. Even thought eventually China was invaded, it did keep the nomads out of the walls for a long time.
2. The Mongols could have killed many more if the walls didn't keep them out for as long as it did.
3. In the end, the materials used to build the wall were cheap.
4. Finally, it became a historical landmark and still attracts visitors.
Until today, people still debate about the Great Wall of China and if it was or wasn't worth the cost.