donjon

1. The central keep, or donjon, known as the White Tower because of its limestone, was begun c.1078 by 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」。
2. To the north, Saint-Denis and its spire; to the west, Saint Cloud and its donjon keep.
   北边是圣德尼及其尖顶，西边是圣克鲁及其圆形主塔。

noun

1. the main tower within the walls of a medieval castle or fortress

   Synonym:    keepdungeon