One of the most characteristic features of a society is the way in which it organizes its time, designating special days and hours for work, religion, rest, recreation and commerce. Socially accepted patterns of temporal organization are essential to the development of communal activities such as festivals, sports, religious ceremonies, market-place trade and industrial production. Once introduced, patterns of temporal organization tend to establish themselves more and more firmly through time as they become rooted in the customs and traditions of the local population. They are only likely to be changed as a result of wide-ranging social, economic and demographic changes affecting the whole fabric of society. Any possible changes in established temporal patterns usually have both advocates and opponents, and actual changes often result from temporary or permanent shifts in the balance of power between different socio-economic groups, or from shifts in opinion promoted by external factors.