Simplify the following text for a Grade 11 native English-speaking person.
Original: In 1481 , Pope Sixtus IV summoned Botticelli and other prominent Florentine and Umbrian artists to fresco the walls of the Sistine Chapel .
Simplified: In 1481 , Pope Sixtus IV summoned him and prominent Florentine and Umbrian artists who had been summoned to fresco the walls of the Sistine Chapel .