From sub Saharan Africa to the west coast tribes of Canada to the Mardi Gras of Rio, New Orleans and Venice, masks define realities - of religious belief, of healing power, of theatre and entertainment, of concealment and of memorialisation in death. They have been around as long as humanity and they evoke both fascination and fear. Mike Williams traces the power and culture of masks and asks why we have them and what they mean for us.

(Image: A group wearing masks of legendary heroes as they perform a dance in Minhe County of Qinghai Province, north-west China. Credit: Getty Images)