The history of the Castle of Spilimbergo mingles with that of the lords of Spilimbergo, the Spengenberg, a family of noble origin from Carinthia, loyal to the Empire, the most notable in the region and among those present in the Parliament of Friuli, "ministeriales" from the Patriarchate of Aquileia.  Relying on their power and prestige, they often came into conflict with the Patriarch and on several occasions conspired against him.

The most famous and dramatic episode occurred in 1350, during the feudal civil war that bloodied Friuli: in the Richinvelda plain, a few miles south of the city, some feudatories who had set off from the Castle of Spilimbergo, led by Spengenberg, confronted and killed the old but energetic Patriarch (later beatified) Bertrand of San Genesio in an ambush. Since then the people from Spilimbergo have been called or nick-named Bertramini or Beltramini.

The castle was attacked many times during the medieval wars between the Venetian and the Friulian lords, withstanding repeated attacks by the da Camino.

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