Complex sentence: The castle was first mentioned in the 12th century but the present fortress was constructed by Godfrey of Hellebeek between 1300 and 1310 as a defense base for Brussels.
Split into simpler sentences: The castle was first mentioned in the 12th century. The present fortress was constructed by Godfrey of Hellebeek between 1300 and 1310 as a defensive base for Brussels.