Clear traces from the Middle Ages have been preserved at Mergentheim Palace. The irregular floor plan of the complex added to later, which was probably founded in the 11th century, goes back to the medieval water-surrounded castle. The modes can still be seen today. A look into the early history is also provided by the preserved elaborate Staufer "Palas" (main building) arcades. They originated in the mid 13th century and were originally part of the former western outer wall of the south wing. Since the 18th century they adorn an inner wall in the south wing.
Since 1527, since the headquarters of the Teutonic Order (Deutscher Orden) was moved to Mergentheim, the demands of the Grand Masters (Hochmeister) on the representative function of the complex increased. The castle was expanded to a Renaissance residence. As in other representative palaces of the age in Southern Germany, Blasius Berwart was commissioned as the architect. The outstanding testimonials to his building activity include the spiral staircase with ornate reliefs on the underside built in 1574.
Between 1730 and 1799 Mergentheim Palace was partially redecorated in the baroque style. A newer, larger Palace Church (Schlosskirche) was built (1730-36) with concave entryway facades and ceiling frescos and stuccowork which realized the baroque idea of an increased three-dimensional effect. From this period two apartments with magnificent ornamental plasterwork in the upper floor of the south and north palace wings have also been preserved. Intricately worked figures from antique mythology adorn ceiling paintings and stucco motifs.