Simplify the following text for a Grade 7 native English-speaking person.
Original: By 212 BC Antiochus III had invaded the domain of Xerxes and defeated him after laying siege to the city of Arsamosata .
Simplified: Xerxes ( died c. 212 BC ) was the King of Sophene and son of Arsames II . During his domination Antiochus III the Great invaded his capital Arsamosata .