The foundation for the "dai-tenshu" (large donjon) measures about 24.8 metres (81 ft) from east to west, and 22.4 metres (74 ft) from north to south, and covers an area the size of the first floor of the "tenshu" of Himeji Castle, which has an area of 550.025 square metres. It has long been believed that there had not been a "tenshu" on the foundation; however, indirect descriptions of a "tenshu" are seen in a few old documents and the existence of an annex for the "tenshu" is indicated on some old maps. The problem is now being studied by various researchers. (Kuroda Nagamasa tried to destroy all the documents which were related to Christianity. Since "tenshu" also means "(Christian) God", it is possible that he destroyed almost all the documents which contained the word "tenshu".)