Fort Willem I, Ambarawa

Fort Willem I, known in Indonesian/Javanese as Benteng Pendem Ambarawa ("Ambarawa sunken fort"), is a 19th-century Dutch fort in Ambarawa, Central Java, Indonesia.

In period of Diponegoro War (1827-1830), Colonel Hoorn, Military Commander in the 2nd division to the crossroads at Bawen (point of junction of the roads connecting Semarang-Yogyakarta and Semarang-Salatiga) instructed the construction of logistic storage, as well several military barracks, to give immediate supply and forces for the war. Simple bamboo sheds was established at this strategic point.

After the War, during the reign of Willem II, the place of the bamboo sheds proved very strategic. So a new modern fort was constructed at the former bamboo sheds area between 1834-1853. In 1840, Ambarawa grew as one of a strategic military outposts along the route between Semarang and Surakarta. The VOC had established several military defense points along this route which connects Semarang - Ungaran - Salatiga and Surakarta. The purpose of the establishments of these defense points was to establish relationship with the Sultanate of Mataram.

From 1853 to 1927 KNIL military barracks were set up in the fort. The private Dutch East Indies Railway Company (NIS) received concession in 1862 to build a rail track connecting Semarang, Surakarta, Magelang and Yogyakarta with a branch toward Fort Willem I. Construction started in 1863 and was completed in 1873. An earthquake occurring on July 16, 1865 damaged some buildings inside the fort. In 1927, Fort Willem I was adjusted from penitentiary of children prisoner into a penitentiary for political prisoner and adult prisoner.

During the period of Japanese occupation, Fort Willem I was converted into an internment camp.

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