Simplify the following text for a Grade 8 native English-speaking person.
Original: Giotto 's masterwork is the decoration of the Scrovegni Chapel in Padua , commonly called the Arena Chapel , completed around 1305 .
Simplified: Giotto 's greatest work is the decoration of the Scrovegni Chapel in Padua , finished around 1305 . The building is sometimes called the `` Arena Chapel '' because it is on the site of an Ancient Roman arena .