The "Alte Wache", as the main guardhouse is popularly known, was built in 1819 during the reign of Prince Heinrich XIX Reuß of the older line (1790-1836). Like the Lower Castle opposite, it has a classicist simplicity. The protruding gable, in the front of which the great coat of arms of the Reuss princes of the older line is emblazoned with the initials "H XIX FR" (Henry the Nineteenth, Prince Reuss), is supported by four Doric columns. The coat of arms is held by two lions of the bailiffs of Plauen. The two cranes indicate that the dominion of Kranichfeld belonged to the Reusses for a time.

Until 1866, the military of Reuss-Greiz provided guard duty here and from this time until the First World War a detachment of the Gera Infantry Regiment 96. In 1918, the Greiz main guard lost its purpose due to the abdication of the prince in the November Revolution.

Its function changed several times in the following years. For example, the tourist information office was based in the "Alte Wache" until 1993. The main guardhouse is currently used as a wedding hall by the Greiz registry office.