When finished in 1869 Rijnauwen was the most modern fort in the Netherlands and the first to be built according the polygonal system. It was also the largest fort of the New Water Line, covering an area of about 31 hectares. It had to defend a very important plateau east of Utrecht. This area was strategically of the highest importancy for the New Water Line, since inundations were hardly possible here.

After the experiences of the French-Prussian war of 1870-71 the fort was modified extensively. One of the modifications was the construction of barracks in the center of the front. The building consisted of three levels: the troop quarters at the first floor, gun shelters at the upper level and magazines in between. This is one of the few decorated building with the use of yellow bricks. In the Dutch forts utility was more important than appearance.