The stone flagpole pedestal is located in the front southwest corner of the Hall of Imperial Peace (钦安殿：Qin An Dian) , and built on a marble base (figure 1). The four sides of the pedestal are engraved with double dragons frolicking with magic pearl (figure 2). The catalog number 204008 of the Palace Museum collection is clearly visible (figure 3). Checked it out online, it’s called a copper-plated flagpole pavilion, and it looks like the data entry is wrong. Later, I saw Guan Jing’s paper “sincerely pray for the Hall of Imperial Peace Dojo” , it turns out that the description here is not about the flagpole itself, but the top structure of the pole, the baoding (literally, “treasure top”) . According to Guan Jing, the flagpole was recorded as: “Five Dragons Holding the Flagpole“. The pole is nine zhang, five chi long (about 31 meters). On the top of the pole is a “gold-plated copper square pavilion with double eaves” baoding. There is a silver box in the baoding, which contains “the Celestial Venerable father of the Primordial Beginning tells the wonderful Sutra of northern Zhenwu” (元始天尊说北方真武妙经) and “Primal Beginning Boundless Salvation Highest Level Mystical Scripture“ (元始无量度人上品妙经).
The four corners of the marble base have turtle (southeast) , fish (southwest) , crab (northwest) and shrimp (northeast) patterns (figure 4). In the Hall of Imperial Peace, there is a bronze statue of Zhenwudadi (真武大帝), also known as Xuanwu, the God of water . Therefore, the base engraved with these “shrimp soldiers and crab generals” is a matter of course.
“Originally, the stone pedestal held a wooden pole that rose above the Forbidden City. If you look southeast from the White Pagoda（白塔） of Beihai Park（北海公园）, only this pole was picked out from the yellow tiles and green shades, and becoming a visible symbol of the Imperial Garden（御花园）.”
From the photo of Lin Jing, you can clearly see the flagpole (figures 5, 6). The photos were taken in 1901 and 1920s . High flagpole can also be seen in the photos taken by Gamble from Coal Hill (景山) in 1918 click to view and from the Palace of Gathered Elegance (储秀宫) in 1924-1927 click to view  . And Morrison’s 1933-1946 photo did not see the flagpole , click to view. Therefore, we can conclude that the flagpole disappeared between 1933 and 1946. It is not known why the flagpole was removed or where it is kept today. No relevant information was found.
In Guan Jing’s paper, also provides an old photo, captioned as “the scene of the construction site of the Five Dragons Holding the Flagpole”, and noted at the end of the Qing Dynasty. However, it is clear from the photo that the base of the flagpole has already decayed. Based on the above conclusions, this photo should show the removal of the flagpole between 1933 and 1946.
下面这张照片翻拍自单霁翔的影集《故宫藏影——西洋镜里的皇家建筑》，为甘博（Sidney D. Gamble ）在1924-1927年间所摄：553A_3205）。从中可以看到幡杆的更多细节。
This photo below is from Shan Jixiang’s photo album Hidden Shadows in the Forbidden City: Imperial Architecture in the Shot of Foreigners. . The original photograph was taken by Sidney D. Gamble between 1924-1927, photo ID:553A_3205. Details of the flagpole can be seen in this photo.
[306-1751 and 553-3205], Sidney D. Gamble Photographs, David M. Rubenstein Rare Book & Manuscript Library, Duke University.
 [W86461-1] , Hedda Morrison Photographs, Harvard University, Harvard College Library Harvard-Yenching Library