Supplementary to the trading facilities afforded by weekly markets, special privileges were enjoyed during the time of annual fairs, for the holding of which authority was frequently conferred on burghs. The burgh of Glasgow was established sometime between 1175 and 1178.

A few years after that, probably between the years 1189-98, King William authorised Bishop Jocelyn and his successors to have a fair at Glasgow, for eight full days from the octaves of SS.Peter and Paul. The fixing of this fair was in keeping with medieval custom, fairs being usually appointed in connection with saints' days or other religious festivals, or in commemoration of the dedication of churches.

The cathedral church of Glasgow, built by Bishop John, was consecrated on 7 July 1136,and it was probably the practice for tradesmen and merchants to bring their wares for sale to a convenient spot in the vicinity of the church on the anniversary of that event.

The practice of observing the octave continued until 1744. In that year, the magistrates and council, taking into consideration that 'the Sabbath intervening in these eight days stops and interrupts the course of the fair' resolved that in future, instead of the fair beginning on a fixed day in the calendar, it should begin on the first Monday of July and finish on the following Saturday.

No subsequent regulation on the subject had been passed by 1921, but the transition from the Julian to the Gregorian calendar in 1752 operated indirectly in producing a change, and the fair now began on the second Monday of the month.