Fillet (clothing)
A fillet was originally worn in classical antiquity, especially in cultures of the Mediterranean, Levant and Persia, including Hellenic culture. At that time, a fillet was a very narrow band of cloth, leather or some form of garland,  frequently worn by athletes. It was also worn as a sign of royalty and became symbolized in later ages as a metallic ring which was a stylized band of cloth. Greeks called it Diadema (διάδημα) and although most Roman Emperors didn't wear it, after Caesar refused it when offered him by Antonius, except in a few cases, Constantine the Great adopted the Greek emblem of royalty. Before the diadem was worn by the Roman emperors as a symbol of sovereignty, it was used as a head-dress by Roman women. Later, in medieval times, a fillet was a type of headband worn by unmarried women, in certain monk hoods, usually with a wimple or barbette. This is indicated in the sign language of said monks (who took oaths of silence), wherein a sweeping motion across the brow, in the shape of a fillet, indicated an unmarried woman. Gallery

See also
 Diadem
 Tainia
 Wreath

References

13th-century fashion
14th-century fashion
Headgear
Crowns (headgear)