Petrus Gyllius or Gillius (actually Pierre Gilles) (1490–1555) was a French natural scientist, topographer and translator.
Gilles was born in Albi. He travelled and studied the Mediterranean and Orient, producing such works as De Topographia Constantinopoleos et de illius antiquitatibus libri IV,Cosmæ Indopleutes and De Bosphoro Thracio libri III, and a book about the fishes of the Mediterranean Sea. Among others, he spent the years 1544 to 1547 in Constantinople, where he had been sent by the French King Francis I in order to find ancient manuscripts. In fact he discovered a manuscript of the geographical work of Dionysius of Byzantium and made a Latin paraphrase of it. Most of his books were published after his death by his nephew. He also translated Claudius Aelianus in 1533. He died in Rome of malaria, while he was following his patron, Cardinal Georges d'Armagnac.