Complex sentence: Because of unstable foundations and the whole hill, enhancement walls and barriers were made from the 17th to the 19th century on north and south sides of the hill to prevent any damage to the building.
Split into simpler sentences: Because of unstable foundations and the whole hill, enhancement walls were built in the 17th century. Additional barriers were made from the 17th to the 19th century on north and south sides of the hill to prevent any damage to the building.