Simplify the following text for a Grade 8 native English-speaking person.
Original: Of its many works of art may be mentioned the magnificent marble tomb of the founder and his wife , the empress Cunigunde , considered the masterpiece of the sculptor Tilman Riemenschneider , and carved between 1499 and 1513 .
Simplified: One of the most magnificent ones is the marble tomb of Henry II , the founder of the cathedral , and his wife , the empress Cunigunde . It took the famous sculptor Tilman Riemenschneider 14 years to carve : between 1499 and 1513 .