Complex sentence: The Norman lord Brian Fitzgerald had been riding through the lands neighbouring his castle in Danore when he came across members of the Mac Geoghan clan who had long disputed De Lacy's claim to the lands.
Split into simpler sentences: The Norman lord Brian Fitzgerald had been riding through the lands neighbouring his castle in Danore. He came across members of the Mac Geoghan clan who had long disputed De Lacy's claim to the lands.