Martello Fort (round fort) was one of Dutch Citadel’s and surveillance tower. Martello fort and Surveillance tower were circular with its diameter of 23 meters and 2.5 meters of thickness still look solid and robust. Rows of large and small windows were mounted to this side of wall. There are seven chambers at the ground floor partitioned by bricks walls.
One of the locked rooms served as a ammunition storage. A circular wall stood at the center of clean water container in which the water was used to drink and cook for the officers on guard. The surveillance tower was supposedly constructed of two stories since there were holes for floor beams. There were seven chambers on the second story. The chambers at the second story were presumably sleeping chambers as well as surveillance rooms.
The fortress was constructed of bricks thus it only managed to operate till 1878 and it was used solely as gunpowder storage. It begun to deteriorate after the earthquake and tsunami caused by eruption of Mt. Krakatau at 1883 and was deserted since 1908 other than as a center for historical research. There were also other Fort Martello other than at Bidadari such as one located at Kerkhof (Kelor ) and Onrust.