Simplify the following text for a Grade 4 native English-speaking person.
Original: In 1691 , he wrote the music for what is sometimes considered his dramatic masterpiece , King Arthur , with the libretto by Dryden and first published by the Musical Antiquarian Society in 1843 . Another one of Purcell 's operas is King Arthur , or The British Worthy in 1691 .
Simplified: In 1691 , he wrote King Arthur , also written by Dryden .