Simplify the following text for a Grade 13 native English-speaking person.
Original: Sejanus began a series of purge trials of senators and wealthy equestrians in the city , removing those capable of opposing his power as well as extending the imperial ( and his own ) treasury .
Simplified: In 29 Sejanus began a series of purge trials of senators and wealthy equestrians in the city , removing those capable of opposing his power , adding to the imperial ( and his own ) treasury .