The longest wall in the world is the Great Wall of China.

This wall is one of the most famous man-made structures in history. It was built over many centuries to protect Chinese kingdoms and empires from invasions by enemies. The wall stretches across deserts, mountains, and grasslands in northern China.

The total length of the Great Wall is more than 21,000 kilometers. That is more than the distance from Pakistan to the United States and back. It is made of bricks, stones, wood, and other materials, and some parts of it were built as early as the 7th century BC.

The wall is not a single straight line. It is made up of many walls and sections built by different dynasties, especially the Ming Dynasty. The wall includes watchtowers, fortresses, and passes, which helped soldiers protect the region.

Today, the Great Wall is a symbol of China long history and strength. It is a UNESCO World Heritage Site and attracts millions of tourists every year from around the world.

So, the correct answer is Wall of China.