Complex sentence: His byname Gulban derives from Benn Gulban (the mountain of Benbulban) in Co.Sligo, from which center the sons of Niall set out upon their conquest of the north.
Split into simpler sentences: His byname Gulban derives from Benn Gulban (the mountain of Benbulban) in Co.Sligo. From which center the sons of Niall set out upon their conquest of the north.