The nobleman joined the Teutonic Order (Deutscher Orden) in 1566 and made a career for himself there, rising from the kitchener at the Order house in Ellingen to become involved in the politics of the Reich, in which he played a role as the advocate of Hapsburg interests and as the imperial Commissioner. In 1590 Westernach received the Kapfenburg commendam. In the years that followed he had the medieval castle expanded to a representative palace. The Convention of the Teutonic Order (Deutschordenskonvent) elected him to Grand Master and Master of the Teutonic Order in 1625. Westernach is buried in the Palace Church (Schlosskirche) in Bad Mergentheim.
Von Stadion was elected Grand master in the Thirty Years' War in 1627. He met with the imperial general Wallenstein (Albrecht von Waldstein) in 1630 at the Kapfenburg. In 1632 the Kapfenburg was lost following the victory of the Swedish troops and went to Count Georg Friedrich von Hohenlohe until 1634. Stadion died in 1641 in a military camp in Thuringia.
Under Hornstein the Kapfenburg was given the appearance it has today. He was the son of a Hohenzollern nobleman. At the age of 13 he entered the service of the later Grand Master Ludwig Anton von Pfalz-Neuburg as a page and was knighted in 1689 in Ellingen. In 1713, after holding the position of commander at various places, he became commander on the Kapfenburg. In 1717 Hornstein was named governor of the "Ballei" (administrative district) of Franconia, and in 1718 to its Country Commander (Landkomtur). He reigned for 25 years, died in 1745 and was buried in the Mariahilf Chapel (Mariahilfkapelle) in Ellingen.
The son of a master mason from the town of Dürrwangen in Middle Franconia initially worked as a stonecutter during the construction of the pleasure palace of Count von Oettingen in Schrattenhofen under Maximilian von Welsch. In 1711 he entered the service of the Teutonic Order. As its head architect he executed numerous secular and holy buildings. In 1715 he came to the Kapfenburg, remodeled the lower chapel and redesigned parts of the Hohenlohe Building (Hohenlohebau) and of the Westernach Building (Westernachbau). Franz Keller died suddenly in 1724 during his work on the official palace in Absberg, on Ellwangen Palace and on numerous other building projects being planned at that time, including in Mergentheim.
The Viennese stuccoworker entered the service of the Teutonic Order in 1715, when he worked on the Hohenlohe Building and the Chapel of Lorenz (Lorenzkapelle) on the Kapfenburg. He settled in Mergentheim and worked together with Franz Keller in Ellingen. His unreasonable request to become Keller's successor as head architect following death was refused. However, the Commander Karl Heinrich von Hornstein obligated him as a stuccoworker and beginning in 1729 also as head architect. Among other things, he planned and built the Palace Church (Schlosskirche) in Mergentheim, executed stuccowork in the palace there and erected (meanwhile as building director) the Sala terrena on the South side of the palace in Mergentheim. After arguments with the Teutonic Order Roth retired to Mergentheim. He died in 1758 in Gelchsheim in Lower Franconia.
From 1806 to 1807 the son of King Friedrich von Württemberg lived at the Kapfenburg. He received Mergentheim Palace as his residence in 1827 following his marriage to Princess Sophie Dorothee Caroline von Thurn und Taxis. The duke was interested in botany, zoology and foreign cultures. During his numerous journeys in Europe and abroad he completed his ethnographic collections, which he kept at Mergentheim Palace. He was one of the most important naturalists of the 19th century. A fraction of his collection still exists and is kept at the "Lindenmuseum" in Stuttgart. Duke Paul died on 11/26/1860 in Mergentheim and is buried in the Cathedral (Stiftskirche) in Stuttgart.