Osteiner Hof, Baroque city palace at Schillerplatz, Mainz, Germany.

The Osteiner Hof is a baroque city palace on Schillerplatz in the old town of Mainz, with a facade marked by three rounded projections. Stone carvings frame the windows and balcony doors across the entire front of the building.

The palace was built between 1747 and 1752 by architect Johann Valentin Thomann for Franz Wolfgang Damian von Ostein, a member of a powerful Mainz family. After the French Revolutionary wars, it was used as an administrative seat for the department of Mont-Tonnerre.

Every year on November 11 at 11:11 in the morning, the official start of Mainz's carnival season is announced from the balcony of the building. At that moment, the square fills with people gathered to watch the ceremony.

The palace stands at Schillerplatz 1 in Mainz's old town and can be seen from the open square, which gives a clear view of the full facade. The best time to see the building in a lively context is around November 11, when crowds gather in front of it.

The building kept the nickname "Gouvernement" from 1854 to 1859, when the future Emperor Wilhelm I served as military governor of Mainz. In 1914, General Hugo von Kathen announced the outbreak of World War I to the crowd from the central balcony.