Simplify the following text for a Grade 7 native English-speaking person.
Original: In 1546 part of the island was handed over to Cosimo I de ' Medici , who fortified Portoferraio and renamed it `` Cosmopoli '' , while in 1577 the rest of the island was returned to the Appiani .
Simplified: He fortified Portoferraio and renamed it `` Cosmopoli '' . In 1577 , the rest of the island was returned to the Appiani .