From 770 B.C. through 476 B.C. was the Spring and Autumn Period of China. During the Period, princes that held land from the Zhou Kingdom made themselves states. Among all the 149 states, the most powerful were the Qi, Jin, Chu, Qin, Lu and Zheng States.
For the wide use of iron tools and farm cattle, the social production of this period progressed greatly. The higher-rank people started to gain private croplands. The land was privatized, and the basic social system of the day, i.e. the Well Field System, began to collapse, which cracked Zhou Kingdom's leadership over its princes and caused among them wars for domination.
To conquer other states, stronger ones made frequent wars upon others. Only a few out of the more than a hundred had finally survived, and were anxious for a new round of war. These states included Qin, Wei, Yan, Zhao, Han, Qi, Chu, also referred to as "the Seven Powers", and others less strong. And the history came to the Warring States Period (B.C. 475 ~ 221).
The social production of this Period continued to grow. The advancing in agriculture and handicraft gave rise to thriving cities acting as marketplaces. The architecture of this time also improved remarkably and made it possible to build solider constructions of better structures in more flexible steps. On the other hand, wars went on unabatedly between the states, some of which at the same time were harassed by minority nationalities from the north. Hence the states built walls around important cities, especially their capitals.
A latest excavation has revealed that the wall-surrounded capital Linzi of the Qi State in the Warring States Period was four kilometers from east to west, and five kilometers from north to south. Palaces to rulers lay inside. Distributed in the city were workshops selling instruments made by way of smelting iron ores, casting bronze, abrading and carving bones and the like. It is recorded in Shi Ji, a great historical literature, that Linzi had over 700,000 families (the unit ancient Chinese used to count population) and was "so crowed with people and vehicles that they could hardly go without brushing each other".
The city Xiadu of the Yan State was eight kilometers from east to west, and four kilometers from north to south. The capital Handan of Zhao was three and four kilometers from east to west and from north to south.Because walls around cities proved excellent defense, the states wanted to utilize this advantage widely. Hence they built walls on the borders and joined them up with natural barriers like large embankments and steep mountain ridges.The building of walls expensed countless labors. But they were undoubtedly grand constructions even seen today.
