The central keep or donjon known as the white tower because of its limestone was begun c. 1078by william I the conqueror inside the roman city wall.

约1078年由征服者威廉一世开始在罗马城墙内侧建造一座中央城楼「白塔」（因以石灰岩建造而得名）。

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The Economics Research Associates (ERA), who helped promote the Tower of London and Stonehenge, has been appointed to improve tourist numbers to the Roman wall.

BBC: North site can be 'next Stonehenge'