The Great Wall of China was built over centuries by Chinas emperors to protect their territory. The materials used to construct the wall depended on the local resources available. When building the Great Wall on mountains, stones were used from the mountains, while in the plains, the materials used were earth, bricks, and lime. Even branches of willow trees were used with sand when the Great Wall was built across the deserts. The construction materials of the Great Wall were mainly earth, stone, brick, lime, and wood. Before the Sui Dynasty (581–618), most sections were built with earth, stone, sand, lime, and wood. Most of the Great Wall sections were built with earth because of the low technology at that time. With the development of brick-making techniques, bricks were used from the Tang Dynasty (618 – 907 AD) onwards. Therefore, the Great Wall of China was made of a combination of earth, bricks, stones, lime, and wood.