Complex sentence: Originally a Medieval fortress, probably built in the 11th century and rebuilt in the 12th century, it acquired its present outline with an almost complete overhaul in the 15th century, whereas the majority of the buildings date to the 16th and 17th centuries.
Split into simpler sentences: Originally a medieval fortress, it was probably constructed in the 11th century and rebuilt in the 12th century. It acquired its present outline with an almost complete overhaul in the 15th century, whereas the majority of the buildings date to the 16th and 17th centuries.