Simplify the following text for a Grade 10 native English-speaking person.
Original: 651 : Last Sassanid ruler Yazdegerd III then fled eastward from one district to another , until at last he was killed by a local miller for his purse at Merv ( present-day Turkmenistan ) , ending the dynasty .
Simplified: 651 : Last Sassanid ruler Yazdegerd III murdered at Merv , present-day Turkmenistan , ending the dynasty .