The boundaries of each parish were customarily marked by stones and every year, 'Beating the Bounds' took place. This is an ancient custom which is still observed by many English parishes; the roots go back to medieval times when parishes re-affirmed their boundaries by processing round them at Rogationtide, stopping to beat each boundary mark with sticks and to pray for protection and blessings.
The ceremony was also important so as to prevent encroachment by neighbours and to instil a folk memory of the time as to the area of the parish. It is however no longer the tradition to bump the choirboys heads against the marks!
In the case of some City parishes the boundary is in the middle of the River Thames and the beating party have to take to boats to 'beat the mark' in the middle of the river. In more recent times, especially in cities the parishes were marked with either metal or stone plaques affixed to walls.