It is also notable for hosting the Ekhof-Theater [de], one of the oldest theatres in operation in Germany, still featuring the original Baroque machinery for changing the scenery.

The site where Friedenstein stands today, dominating the town of Gotha and its surroundings, was previously occupied by Grimmenstein Castle.

In 1547, the Ernestine branch of the House of Wettin as members of the Protestant Schmalkaldic League had lost the Battle of Mühlberg against the Catholic forces of Emperor Charles V. As a result, Johann Friedrich I, Kurfürst von Sachsen (John Frederick I) was stripped of his title as "Elector of Saxony" (Kurwürde).

In naming the castle Friedenstein (literally "peace-rock"), Ernst made a point of drawing a clear line between this new palace and the warlike history of its predecessor.

When it was finished in 1656, Friedenstein was the first ever Residenz in the Baroque style built on German soil that was completed during the lifetime of the ruler who ordered it.

So after his death in 1675, the Duchy was split in 1680/81 into seven separate territories: Saxe-Gotha-Altenburg, Saxe-Coburg, Saxe-Meiningen, Saxe-Römhild, Saxe-Eisenberg, Saxe-Hildburghausen and Saxe-Saalfeld.

[1]: 9–10 In 1826, after the death of the heirless Friedrich IV, the Duchy was split and Gotha passed to Ernst I of the House of Saxe-Coburg and father of Albert, Prince Consort who was to marry Queen Victoria.

As Alfred's uncle, Prince Arthur, Duke of Connaught, and cousin, Prince Arthur of Connaught, both renounced their right of succession to the Duchy, the title passed to Charles Edward (Karl Eduard), the son of the Duke of Albany, fourth son of Victoria and Albert.

World War I caused a conflict of loyalties for Charles Edward/Karl Eduard, but he sided with Germany, leading the British government to strip him of his titles in the United Kingdom.

[2]: 94 During the time of the German Democratic Republic (GDR), renovation work in the castle began in 1965 and many of the additions of the late 19th and early 20th century were removed from the interior.

[1]: 85 In what became known as the Kunstraub von Gotha [de], in the night from 13 to 14 December 1979, five valuable paintings were stolen from the castle: Frans Hals (Brustbild eines jungen Mannes), Anthony van Dyck (Selbstbildnis mit Sonnenblume), Ferdinand Bol (Alter Mann), Jan Brueghel the Elder (Landstraße mit Bauernwagen und Kühen) und Hans Holbein the Elder (Heilige Katharina).

[1]: 5 The castle built for Ernst I was constructed according to general principles favoured by Protestant rulers in the 17th century.

The simple, unadorned exterior was originally selected to contrast with the palaces of Catholic princes, which at the time were still mostly influenced by the elaborate Renaissance style.

The only major embellishment at Friedenstein were four larger-than-life statues located at the four corners of the palace, showing Moses, Elijah, John the Baptist and Martin Luther.

Other external features were a few reliefs salvaged from the old Grimmenstein and some decoration above the main gate to the courtyard, located in the centre of the north wing.

The austere facades are structured not by ornamental features but only by the symmetrical arrangement of the windows and a cornice running around the whole building between the first and second floors.

The major later change to the external appearance of the palace has been the addition of the two buildings on the left and right of the main wing facing the town, known as Pagenhaus and Wachthaus, added in 1778/79.

The palace sections that have maintained their original use include the chapel and the Geheimes Archiv on the ground floor of the north wing.

Otherwise the ground floor of all the wings housed servants' and storage rooms as well as an armoury, a stable, a mint and a smithy.

The second floor contained the main representatives areas reached by two staircases located at the juncture between the north and the side wings.

The hall was thus demolished and replaced by a new fire wall along with new state apartments: a suite of five rooms each for Duke and Duchess.

Since work was not finished in time for the wedding, the Princess moved into the rooms in the northwest corner and Emil August into the unfinished west wing.

[1]: 20–21 After the change in dynasties, the new Duke Ernst I von Sachsen-Coburg und Gotha had the rooms in the northwest corner redesigned.

Various changes occurred during the long reign of Ernst II: Space for the museum became too tight, so it was decided in 1863 to construct a specialised building.

Despite the work done in the 1860s, the palace was not suitable for running a household in accordance with the demands of a ruling prince, lacking sufficient guest quarters for example.

In 1774, an actor group led by Conrad (or Konrad) Ekhof, called "the father of German acting", came from Weimar to Gotha.

The theatre features a Baroque Kulissenbühne [de] still in working condition, which makes it possible to change the scenery in view of the audience while the curtain is open.

[1]: 27 Major changes in the 20th century were limited to memorials and the areas immediately to the north and south of the castle proper.

In 1947, the statue of the soldier was removed by the Soviet authorities and twenty years later replaced with a memorial to “the victims of fascism”.

[6] The Schlossmuseum currently combines the Baroque and neoclassical state apartments, the Ducal Kunstkammer, the Neue Münzkabinett (numismatic collection) and the Ekhof-Theater.