The construction method of the grey-brick walls was roughly the same as the adobe walls,which was to have the readymade grey-bricks laid up piece by piece,reinforcing the wall by pointing in between the two bricks with glutinous rice or yellow mud or lime in thick liquid form.This method started in the Northern Wei Dynasty as the brick-making technology had made some development then and being applied to the Great Wall,though was less used due to its expensiveness .People began to build the wall gate with brick covered outside,loess filled inside.In the Ming Dynasty,along with the development and popularization of the brick-making technology,the brick firing scale and production increased tremendously ;the quality improved a great deal and the price tended to be popular.Except being widely used in building folk houses and other buildings,the brick had also been extensively used on the ramparts of the Great Wall.The advantage was that the construction went on faster and more convenient,improving the work efficiency.Even more its defense capabilities had further strengthened as a result of the improvement of solidness.It had not only stopped the enemy pushing forward,but also withstood the attacks from opposition weapons.