Geographical location factor. Xi is a famous and prosperous place among the six ancient capitals. It is easy to defend and block near the main road of marching into the Central Plains in minority areas. Xi is bordered by Tongguan in the east, Sanguan in the west, Xiaoguan in the north and Wuguan in the south. These natural passes protect Xi 'an like a natural barrier, which is a place that is easy to defend but difficult to attack.
Traditional factors of capital construction. After several dynasties of governance, Xi 'an has a very superior city defense and economic foundation. So its successive dynasties also wanted to build their capital here.