Брауншвейг-Люнебург
As the Welf princes all carried the ducal title and the territories they ruled were principalities within the Duchy of Brunswick-Lüneburg, their dominions were named after the main castle or town. William spent most of his time at Calenberg Castle from where he administered the territory. As a result, it is probable that the name of the Principality of Calenberg emerged during this time.