*956 AD–1219 AD: "Outer city—Inner city—Imperial city" Mode*

In this period, Kaifeng became the richest city in the world, according to Zhou [40]. Reflecting its continuing status as the capital city, more projects of new constructions and city walls were undertaken, and the form of the whole city changed significantly. In 956 AD, the government began to reconstruct the city walls. There were now three city walls: around the imperial city, around the inner city and finally the outer city wall (Figure 6).

It was within the imperial city that the emperor handled state affairs. Its boundaries can be traced back to the Tang Yashu (Figure 5). Emperor Songtaizong enlarged the imperial city wall and it became 5 li (about 2340 m) in length in this period. The imperial city, which was nearly square in shape, was located north west of the inner city. It was occupied in the Jin dynasty. A new palace, Prince Zhou´s Mansion, was built in the Ming dynasty.

The inner city, which was also almost square, was the second-line defense of the city. The eastern and western lines of the inner-city wall were located beneath the city wall of the Ming and Qing Dynasties. In 1219, Emperor Xuanzong rebuilt the new southern and northern walls of the inner city and, consequently, its old southern and northern walls were subsequently destroyed to a large extent. The old southern wall was buried underground to a depth of about 8 m, whilst, the old northern wall was buried to a depth of about 8.5–9.5 m [41]. These walls are now beneath the city wall of the Ming and Qing Dynasties. The whole inner-city wall was built of brick in the Ming dynasty (Figure 7).

**Figure 6.** The probable borders of the city walls of Kaifeng, 956 AD–1219 AD.

**Figure 7.** The probable borders of the city walls of Kaifeng in the Ming Dynasty.

The outer city wall was 50 li 165 bu (about 29180 m) in length [42]. During several wars and in the post-war period, it suffered significant destruction, perhaps most notably in 1642 AD, when it was completely destroyed by flooding from the Yellow River.
