Fort Armstrong, Illinois

Fort Armstrong (1816–1836), was one of a chain of western frontier defenses which the United States erected after the War of 1812. It was located at the foot of Rock Island, Illinois, in the Mississippi River near the present-day Quad Cities of Illinois and Iowa. It was five miles from the principal Sac and Fox village on Rock River in Illinois. Of stone and timber construction, 300 feet square, the fort was begun in May 1816 and completed the following year. In 1832, the U.S. Army used the fort, as a military headquarters, during the Black Hawk War. It was normally garrisoned by two companies, of United States Army regulars. With the pacification of the Indian threat in Illinois, the U.S. Government ceased operations at Fort Armstrong and the U.S. Army abandoned the frontier fort in 1836.

In 1805, when President Thomas Jefferson sent Lewis and Clark on their expedition into the Louisiana Territory, he also sent Lieutenant Zebulon Pike and Major Stephan H. Long up the Mississippi River to gather data and determine strategic sites for forts. Pike identified one site as the "big island;" Congress agreed with his recommendation, reserving the island for military use in 1809 and naming it Rock Island.

The Sauk considered the island sacred:

This [island] was the best one on the Mississippi, and had long been the resort of our young people during the summer. It was our garden, like the white people have near their big villages, which supplied us with strawberries, blackberries, gooseberries, plums, apples and nuts of different kinds. Being situated at the foot of the rapids, its waters supplied us with the finest fish. In my early life I spent many happy days on this island. A good spirit had charge of it, which lived in a cave in the rocks immediately under the place where the fort now stands. This guardian spirit has often been seen by our people. It was white, with large wings like a swan's, but ten times larger. We were particular not to make much noise in that part of the island which it inhabited, for fear of disturbing it. But the noise at the fort has since driven it away, and no doubt a bad spirit has taken its place.

...
Wikipedia