Complex sentence: Nicholas of Verdun (1130--1205) was a French artist, one of the most famous goldsmiths and enamelists of the Middle Ages, a major figure in Romanesque art, and the leading figure of Mosan art in his day.
Split into simpler sentences: Nicholas of Verdun (1130--1205) was a French artist, one of the most famous goldsmiths and enamelists of the Middle Ages. He was a major figure in Romanesque art, and the leading figure of Mosan art in his day.