It is one of the few examples where a native Scottish magnate built a large-scale fortification, something normally practiced by the incoming Normans.
By 1244, Uilleam had married into the Comyn house, the fastest rising Scoto-Norman family in the Scottish kingdom.
The Comyn-Mar alliance helped fight off the ambitions of the Durwards, who were then in prime favor with the king.
Uilleam and the Comyn Earl of Menteith then launched accusations of treason towards Alan while at the court of Henry III of England at York.
When his wife Isabel (also called Elizabeth) died in 1267, Uilleam married Muriel, the daughter of Maol Íosa II, Mormaer of Strathearn.