Before the arrival of the Teutonic Knights, Koknese was the site of a wooden hill fort inhabited by the Balts. In 1209 Bishop Albert of Riga ordered the construction of a stone castle at the site, naming it Kokenhusen. For the first 50 years of its existence, Koknese was solely used as a defensive fort, but by 1277, Koknese had enough population to receive city rights. Koknese also became a member of the Hanseatic League thanks to its strategic location on the Daugava trade route.
The castle was heavily contested between Polish, Swedish and Russian forces in the 16th and 17th centuries. It changed hands many times, while the native inhabitants endured periodic slaughter, capture, and famine. In 1701, during the Great Northern War, Koknese was finally blown up by retreating forces to avoid the strategic castle falling into advancing Russian hands. The castle was never rebuilt and fell to ruin.
In 1900, a park was established around the castle ruins, and Koknese became a popular summer resort. The area was known for its scenic waterfalls, cliffs, and look-outs. In 1965, the Soviet government built Pļaviņas Hydro Power Plant in the town of Aizkraukle. The reservoir flooded the entire length of the Daugava to Pļaviņas. Koknese Castle, once sitting atop a high bluff, was placed at the river's edge, while the scenic Daugava valley was submerged.
References:Ehrenbreitstein Fortress was built as the backbone of the regional fortification system, Festung Koblenz, by Prussia between 1817 and 1832 and guarded the middle Rhine region, an area that had been invaded by French troops repeatedly before. The fortress was never attacked.
Early fortifications at the site can be dated back to about 1000 BC. At about AD 1000 Ehrenbert erected a castle. The Archbishops of Trier expanded it with a supporting castle Burg Helferstein and guarded the Holy Tunic in it from 1657 to 1794. Successive Archbishops used the castle's strategic importance to barter between contending powers; thus in 1672 at the outset of war between France and Germany the Archbishop refused requests both from the envoys of Louis XIV and from Brandenburg's Ambassador, Christoph Caspar von Blumenthal, to permit the passage of troops across the Rhine.