The Principality of Bayreuth or Margraviate of Brandenburg-Bayreuth was an immediate territory of the Holy Roman Empire, ruled by a Franconian branch of the Hohenzollern dynasty. Since Burgrave Frederick VI of Nuremberg was enfeoffed with the Margraviate of Brandenburg in 1415/17, the Hohenzollern princes transferred the margravial title to their Franconian possessions, though the principality never had been a march. Until 1604 they used Plassenburg Castle in Kulmbach as their residence, hence their territory was officially called the Principality of Kulmbach or Margraviate of Brandenburg-Kulmbach until the Empire's dissolution in 1806.

Plassenburg is a castle in the city of Kulmbach in Bavaria. It is one of the most impressive castles in Germany and a symbol of the city. It was first mentioned in 1135. The Plassenberg family were ministerial of the counts of Andechs and used as their seat the Plassenburg. The House of Guttenberg, a prominent Franconian noble family, traces its origins back to 1149 with a Gundeloh v. Blassenberg (Plassenberg). The name Guttenberg is derived from Guttenberg and was adopted by a Heinrich von Blassenberg around 1310. From 1340, the Hohenzollerns governed from Plassenburg castle their territories in Franconia till 1604. The Plassenburg was fortress and residence for the Hohenzollerns.