Complex sentence: Later, the castle lost its defensive role after the extension of the Royal territories; circa 1450, Robert d'Estouteville transformed the castle into a more comfortable residence by dismantling the keep and adapting the fortifications to the incipient artillery.
Split into simpler sentences: Later, the castle lost its defensive role after the extension of the Royal territories. Around 1450, Robert d'Estouteville transformed the castle into a more comfortable residence by dismantling the keep and adapting the fortifications to the incipient artillery.