Complex sentence: At the start of the Eighteenth Dynasty, only the kings were buried within the valley in large tombs; when a non-royal was buried, it was in a small rock cut chamber, close to the tomb of their master.
Split into simpler sentences: At the start of the Eighteenth Dynasty, only kings were buried within the valley in large tombs. When a non-royal person was buried, it was in a small rock cut chamber, close to the tomb of their master.