Altena (pronunciationⓘ; Westphalian: Altenoa) is a town in the district of Märkischer Kreis, North Rhine-Westphalia, Germany.

Altena Castle was built in the early 12th century, as a stronghold of the older Counts of Berg.

The heir of Arnold was Friedrich de Novus Ponte (Nienbrügge) who changed his title to Isenberg after his new castle in Hattingen.

He was sentenced to death as head of a conspiracy to murder Engelbert I. Archbishop of Cologne, Chancellor of the Holy Roman Empire, Duke of Westphalia and Count of Berg, a close relative, in 1226.

After the execution of his cousin Friedrich de Isenberg in Cologne, he destroyed the Castle of Neinbruegge and took over the possessions of the senior family branch.

During a feud in 1323 between the Prince-Bishop of Münster and the Count of Mark, the Bishop was captured and held for ransom in Altena.

His realm, the United Duchies of Jülich-Cleves-Berg were practically divided into a Catholic and a Protestant part.

The Duchy of Cleves and the counties of Mark and Ravensberg, and the Dominion of Ravenstein were inherited by the Protestant Elector of the Holy Roman Empire, Margrave of Brandenburg, and Duke of Prussia Johann Sigismund of Hohenzollern.

During the Napoleonic occupation of the Rhineland and Westphalia, Altena was re-joined with the now elevated Grand Duchy of Berg.

In May 2017, Chancellor Merkel awarded Altena Mayor Andreas Hollstein the "National Prize for Integration" for taking in 370 refugees, i.e. 100 more than the mandatory quota.

[4][5] Number of inhabitants (December 31) The town's biggest attraction is the castle: Burg Altena.

A complete restoration was undertaken in 1909 to celebrate the 300th anniversary of the Prussian incorporation of the county of Mark into Prussia (Brandenburg).