Tony McAleavy will use a range of contemporary sources to tell the little-known story of Malmesbury Castle.
Although no trace of the castle remains above ground it was an extremely important place in the twelfth century.
The castle was of great strategic significance during the civil war between King Stephen and his cousin, the Empress Matilda, 1139-1154.
It was besieged on several occasions and the outcome of the siege of 1153 allowed Henry II to come to power.
Tea will be served from 2:30pm and the talk will begin at 3pm.