Built: 1627 to 1752
Builders: Elector Georg Friedrich von Greiffenklau zu Vollrads (1626-1629), Matthias von Saarburg under Elector von der Leyen (1675-1678), Knight Grünstein (1751-52)
Style: Late German Renaissance

Archbishop Diether von Isenburg had the previous building, Martinsburg Castle, constructed in 1478. As a fortress and princely residence, it was fortified with walls, a moat, and crenellated corner towers. However, by the 16th century, it no longer met the increased representational needs of the Electors of Mainz.

The castle is the most important secular building in the city, a structure of national significance. With its unusually rich, differentiated structure, especially its windows and bay windows, art historians believe it surpasses even Heidelberg Castle.

Although the castle was built during the Baroque period, it is uniquely influenced by the Mannerist forms of the late German Renaissance. There are few comparable buildings of such significance. That is why the eminent art historian Georg Dehio concluded as early as 1906 that it was "... of a refined and distinguished culture that cannot be found again in the German Renaissance."

The facades of the Electoral Palace with their characteristic decorative elements have been preserved. Behind them, the north wing of the palace is now a congress and event venue. The Roman-Germanic Central Museum is also located here.

Television viewers are particularly familiar with the Great Hall of the city's most important secular building: this is where the annual carnival session "Mainz bleibt Mainz, wie es singt und lacht" (Mainz remains Mainz, as it sings and laughs) takes place.